EN ISO 9920:2009

SLOVENSKI STANDARD
01-junij-2010
Nadomešča:
SIST EN ISO 9920:2008
Ergonomija toplotnega okolja - Ocenitev toplotne izolativnosti in odpornosti
oblačil proti vodni pari (ISO 9920:2007, popravljena različica 2008-11-01)
Ergonomics of the thermal environment - Estimation of thermal insulation and water
vapour resistance of a clothing ensemble (ISO 9920:2007, Corrected version 2008-11-
01)
Ergnomie der thermischen Umgebung - Abschätzung der Wärmeisolation und des
Verdunstungswiderstandes einer Bekleidungskombination (ISO 9920:2007, Korrigierte
Fassung 2008-11-01)
Ergonomie des ambiances thermiques - Détermination de l'isolement thermique et de la
résistance à l'évaporation d'une tenue vestimentaire (ISO 9920:2007, Version corrigé
2008-11-01)
Ta slovenski standard je istoveten z: EN ISO 9920:2009
ICS:
13.180 Ergonomija Ergonomics
61.020 Oblačila Clothes
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EUROPEAN STANDARD
EN ISO 9920
NORME EUROPÉENNE
EUROPÄISCHE NORM
June 2009
ICS 13.180; 61.020 Supersedes EN ISO 9920:2007
English Version
Ergonomics of the thermal environment - Estimation of thermal
insulation and water vapour resistance of a clothing ensemble
(ISO 9920:2007, Corrected version 2008-11-01)
Ergonomie des ambiances thermiques - Détermination de Ergnomie der thermischen Umgebung - Abschätzung der
l'isolement thermique et de la résistance à l'évaporation Wärmeisolation und des Verdunstungswiderstandes einer
d'une tenue vestimentaire (ISO 9920:2007, Version corrigé Bekleidungskombination (ISO 9920:2007, Korrigierte
2008-11-01) Fassung 2008-11-01)
This European Standard was approved by CEN on 16 May 2009.
CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European
Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references concerning such national
standards may be obtained on application to the CEN Management Centre or to any CEN member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by translation
under the responsibility of a CEN member into its own language and notified to the CEN Management Centre has the same status as the
official versions.
CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Cyprus, Czech Republic, Denmark, Estonia, Finland,
France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal,
Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland and United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
Management Centre: Avenue Marnix 17, B-1000 Brussels
© 2009 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 9920:2009: E
worldwide for CEN national Members.

Contents Page
Foreword .3

Foreword
The text of ISO 9920:2007, corrected version 2008-11-01 has been prepared by Technical Committee
ISO/TC 159 “Ergonomics” of the International Organization for Standardization (ISO) and has been taken over
as EN ISO 9920:2009 by Technical Committee CEN/TC 122 “Ergonomics” the secretariat of which is held by
DIN.
This European Standard shall be given the status of a national standard, either by publication of an identical
text or by endorsement, at the latest by December 2009, and conflicting national standards shall be withdrawn
at the latest by December 2009.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. CEN [and/or CENELEC] shall not be held responsible for identifying any or all such patent rights.
This document supersedes EN ISO 9920:2007.
According to the CEN/CENELEC Internal Regulations, the national standards organizations of the following
countries are bound to implement this European Standard: Austria, Belgium, Bulgaria, Cyprus, Czech
Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia,
Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain,
Sweden, Switzerland and the United Kingdom.
Endorsement notice
The text of ISO 9920:2007, corrected version 2008-11-01 has been approved by CEN as a EN ISO 9920:2009
without any modification.
INTERNATIONAL ISO
STANDARD 9920
Second edition
2007-06-01
Corrected version
2008-11-01
Ergonomics of the thermal
environment — Estimation of thermal
insulation and water vapour resistance of
a clothing ensemble
Ergonomie des ambiances thermiques — Détermination de l'isolement
thermique et de la résistance à l'évaporation d'une tenue vestimentaire

Reference number
ISO 9920:2007(E)
©
ISO 2007
ISO 9920:2007(E)
PDF disclaimer
This PDF file may contain embedded typefaces. In accordance with Adobe's licensing policy, this file may be printed or viewed but
shall not be edited unless the typefaces which are embedded are licensed to and installed on the computer performing the editing. In
downloading this file, parties accept therein the responsibility of not infringing Adobe's licensing policy. The ISO Central Secretariat
accepts no liability in this area.
Adobe is a trademark of Adobe Systems Incorporated.
Details of the software products used to create this PDF file can be found in the General Info relative to the file; the PDF-creation
parameters were optimized for printing. Every care has been taken to ensure that the file is suitable for use by ISO member bodies. In
the unlikely event that a problem relating to it is found, please inform the Central Secretariat at the address given below.

©  ISO 2007
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by any means,
electronic or mechanical, including photocopying and microfilm, without permission in writing from either ISO at the address below or
ISO's member body in the country of the requester.
ISO copyright office
Case postale 56 • CH-1211 Geneva 20
Tel. + 41 22 749 01 11
Fax + 41 22 749 09 47
E-mail copyright@iso.org
Web www.iso.org
Published in Switzerland
ii © ISO 2007 – All rights reserved

ISO 9920:2007(E)
Contents Page
Foreword. v
Introduction . vi
1 Scope . 1
2 Terms and definitions. 1
3 Application of this International Standard . 5
4 Estimation of thermal insulation of clothing ensemble based on tables and with values
measured on a standing thermal manikin.7
4.1 General. 7
4.2 Insulation values of complete ensembles. 8
4.3 Ensemble thermal insulation values based on individual garments . 8
4.4 Complete ensemble insulation corrected for small differences in composition . 8
4.5 Calculation of thermal insulation for clothing ensembles . 9
4.6 Calculation of thermal insulation for individual garments. 9
5 Estimation of clothing area factor. 10
6 Estimation of surface (or boundary) air layer insulation. 10
7 Estimation of water vapour resistance. 12
7.1 General. 12
7.2 Estimation of vapour resistance of clothing ensembles based on tables with values
measured on standing thermal manikin. 12
7.3 Estimation of vapour resistance of clothing ensemble based on its relation with dry heat
resistance . 12
8 Influence of body movement and air movement on the thermal insulation and vapour
resistance of a clothing ensemble . 13
8.1 General. 13
8.2 Correction of clothing insulation . 13
8.3 Correction of clothing vapour resistance .18
8.4 Activities other than walking . 20
8.5 Relative air velocity . 20
9 Other factors influencing clothing insulation. 22
9.1 General. 22
9.2 Posture. 22
9.3 Effect of seats . 22
9.4 Effect of pressure . 22
9.5 Wetting. 22
9.6 Washing . 22
Annex A (normative) Thermal insulation values for clothing ensembles . 23
Annex B (normative) Thermal insulation values for individual garments. 46
Annex C (normative) Vapour permeability index values for clothing ensembles. 73
Annex D (informative) Measurement of thermal insulation and water vapour resistance of clothing
ensembles on a thermal manikin . 88
Annex E (informative) Measurement of thermal insulation and water vapour resistance of a
clothing ensemble on human subjects . 94
Annex F (informative) Different expressions for the thermal insulation of clothing. 96
Annex G (informative) Estimation of the heat exchanges for reflective clothing. 98
ISO 9920:2007(E)
Annex H (informative) Guidance on the determination of the covered body surface area. 100
Bibliography . 102

iv © ISO 2007 – All rights reserved

ISO 9920:2007(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies
(ISO member bodies). The work of preparing International Standards is normally carried out through ISO
technical committees. Each member body interested in a subject for which a technical committee has been
established has the right to be represented on that committee. International organizations, governmental and
non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the
International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of technical committees is to prepare International Standards. Draft International Standards
adopted by the technical committees are circulated to the member bodies for voting. Publication as an
International Standard requires approval by at least 75 % of the member bodies casting a vote.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. ISO shall not be held responsible for identifying any or all such patent rights.
ISO 9920 was prepared by Technical Committee ISO/TC 159, Ergonomics, Subcommittee SC 5, Ergonomics
of the physical environment.
This second edition cancels and replaces the first edition (ISO 9920:1995), which has been technically revised.
It includes major changes to the sections on clothing vapour resistance as well as those dealing with the
effects of air movement and body motion on clothing insulation and vapour resistance.
This corrected version of ISO 9920:2007 incorporates the following corrections.
⎯ A value and a symbol missing from Equation (38) have been reinstated.
⎯ In Equation (15), the multiplication symbol has been substituted for an (incorrect) asterisk.
⎯ In Figure A.1, traditional Korean garments erroneously captioned “China” and “Sokchina” have been
corrected to read Chima and Sokchima.
⎯ In Equation (F.8), the subscript of the second representation of “I ” has been changed to I .
cl cli
⎯ In the description of symbol H given with Equation (F.1), the minus sign missing from the superscript
−2
attached to the unit W⋅m has been inserted.
⎯ “Mean skin temperature”, given as the description for t with Equation (G.6), has been corrected to
cl
“mean outer clothing surface temperature”.
⎯ In a number of instances, “weight” has been changed to the accepted ISO term, mass.
⎯ Values in Table A.2, No. 134 for I and I have been corrected.
cl T
⎯ Introductory text similar to that present in the first edition has been reinstated in Annex A, and a new
introductory text has been added to Annex C.
⎯ Some minor editorial corrections and additions have been made.

ISO 9920:2007(E)
Introduction
This International Standard is one of a series of International Standards intended for use in the study of
thermal environments. It is a basic document for evaluation of the thermal characteristics of a clothing
ensemble (thermal insulation and water vapour resistance). It is necessary to know these values when
evaluating the thermal stress or degree of comfort provided by the physical environment according to
standardized methods. The thermal characteristics determined in this International Standard are values for
steady-state conditions. Properties like “buffering”, adsorption of water and similar are not dealt with.
The emphasis in this International Standard is on the estimation of the thermal characteristics. The heat and
vapour resistance may also be measured directly, and this is discussed in the annexes.
This International Standard does not deal with the local thermal insulation on different body parts, nor the
discomfort due to a non-uniform distribution of the clothing on the body.
Man’s thermal balance in neutral, cold and warm environments is influenced by the clothing worn. For
evaluating the thermal stress on human beings in the cold (IREQ, see ISO/TR 11079, insulation index),
neutral environments (PMV-PPD, see ISO 7730, indices) and the heat (predicted heat strain, see ISO 7933,
index), it is necessary to know the thermal characteristics of the clothing ensemble, i.e. the thermal insulation
and the water vapour resistance.

vi © ISO 2007 – All rights reserved

INTERNATIONAL STANDARD ISO 9920:2007(E)

Ergonomics of the thermal environment — Estimation of
thermal insulation and water vapour resistance of a clothing
ensemble
1 Scope
This International Standard specifies methods for estimating the thermal characteristics (resistance to dry heat
loss and evaporative heat loss) in steady-state conditions for a clothing ensemble based on values for known
garments, ensembles and textiles. It examines the influence of body movement and air penetration on the
thermal insulation and water vapour resistance.
This International Standard does not
⎯ deal with other effects of clothing, such as adsorption of water, buffering or tactile comfort,
⎯ take into account the influence of rain and snow on the thermal characteristics,
⎯ consider special protective clothing (water-cooled suits, ventilated suits, heated clothing), or
⎯ deal with the separate insulation on different parts of the body and discomfort due to the asymmetry of a
clothing ensemble.
2 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
2.1
thermal insulation
I
2 −1
resistance to dry heat loss between two surfaces, expressed in square metres Kelvin per watt (m ⋅ K ⋅ W )
NOTE 1 In this International Standard it is considered as the equivalent uniform thermal resistance, or thermal
insulation, on a human body. This is the clothing heat resistance (thermal insulation) that, when uniformly covering the
whole body surface (including hands, face, etc.), would result in the same heat loss as the actual, possibly non-uniform,
clothing heat resistance. This heat resistance is the quotient of the temperature gradient between the surfaces (the driving
force) over the dry heat loss per unit of body surface area (the flux):
temperature gradient
I= (1)
heat loss per unit of body surfacearea
For the human body, this resistance can be divided into specific layers, as illustrated in Figure 1 (see also Annex F).
NOTE 2 Because of the special definition of thermal insulation in this International Standard, it is usually expressed
in clo, the unit of thermal insulation of clothing. Although it can be converted into SI units in similar fashion to the thermal
2 −1
insulation of, for example, textile samples [symbol: R ; 1 clo = 0,155 (m ⋅ K ⋅ W )], the meaning is not the same.
ct
ISO 9920:2007(E)
2.1.1
total insulation
I
T
thermal insulation from the body surface to the environment (including all clothing, enclosed air layers and
boundary air layer) under reference conditions, static
See Figure 1.
NOTE Based on Equation (1), it is expressed as:
tt−
sk o
I = (2)
T
H
where
t is the mean skin surface temperature, in degrees Celsius;
sk
t is the operative temperature, in degrees Celsius (in most cases equal to the air temperature, t );
o a
H is the dry heat loss per square metre of skin, in watts per square metre.
2.1.2
basic insulation
intrinsic insulation
I
cl
thermal insulation from the skin surface to the outer clothing surface (including enclosed air layers) under
reference conditions, static
See Figure 1.
NOTE Based on Equation (1), it is expressed as:
tt−
sk cl
I = (3)
cl
H
where t is the mean outer clothing surface temperature, in degrees Celsius.
cl
2.1.3
air insulation
I
a
thermal insulation of the boundary (surface) air layer around the outer clothing or, when nude, around the skin
surface
See Figure 1.
NOTE 1 Based on Equation (1), it is expressed as
tt−
cl o
I = (4)
a
H
NOTE 2 The dry heat loss is composed of radiant and convective heat loss (see Annex G). These heat transfers
through the clothing layers are not considered separately in this International Standard; for the air layer, they can be
considered separately. The alternative representation is then:
I = (5)
a
hh+
cr
2 © ISO 2007 – All rights reserved

ISO 9920:2007(E)
where
−2 −1
h is the convective heat transfer coefficient, in watts per square metre Kelvin (W ⋅ m ⋅ K );
c
−2 −1
h is the radiative heat transfer coefficient, in watts per square metre Kelvin (W ⋅ m ⋅ K ).
r
−1
NOTE 3 Such values are defined for standardized conditions (static body, wind still, i.e. speed < 0,2 m ⋅ s ). When air
movement is present, or when the body moves, this will affect the insulation (typically lowering it), in which case, it is
referred to as resultant or dynamic heat resistance.

Key
1 surface (or boundary) air layer
2 enclosed air layer
3 clothing
4 body
Figure 1 — Schematic representation of total, basic and air insulations
2.1.4
clothing area factor
f
cl
ratio of the outer surface area of the clothed body to the surface area of the nude body
NOTE 1 The outer surface area of a clothed person, A , is greater than the surface area of a nude body, A . Their
cl Du
ratio is therefore larger than 1:
A
cl
f = (6)
cl
A
Du
NOTE 2 Basic and air insulation do not simply add up to total insulation. This is explained by the difference in surface
area between the outer clothing surface and the skin surface. Owing to this higher surface area, the insulative effect for
the body of the air insulation is reduced the thicker the clothing (the larger the outer clothing surface area):
I
a
II=+ (7)
Tcl
f
cl
ISO 9920:2007(E)
2.1.5
resultant total insulation
dynamic total insulation
I
T,r
actual thermal insulation from the body surface to the environment (including all clothing, enclosed air layers
and boundary air layers) under given environmental conditions and activities
NOTE It is the total insulation (I ) value in actual situations (as opposed to reference conditions), including the effects
T
of movements and wind. Values for Ι given in this International Standard and in most of the literature are obtained on a
T
thermal manikin which remains static in a low wind condition, and such values need to be corrected for wind and
movement effects.
2.1.6
resultant basic insulation
dynamic basic insulation
I
cl,r
actual thermal insulation from the body surface to the outer clothing surface (including enclosed air layers)
under given environmental conditions and activities
NOTE It is the basic (intrinsic) insulation (I ) value in actual situations (as opposed to reference conditions), including
cl
the effects of movements and wind.
2.1.7
effective insulation
I
clu
increase in insulation provided to a thermal manikin by a single garment compared to the nude manikin
insulation
NOTE For insulation of individual garments, the term effective thermal insulation is used (I ). The effective thermal
clu
insulation of individual garments making up the ensemble (see Table B.2) is determined on a manikin wearing only that
single garment as:
tt−
sk o
I =−II= −I (8)
clu T a a
H
where
2 −1
I is the total thermal insulation of the garment, in square metres Kelvin per watt (m ⋅ K ⋅ W ) or in clo;
T
t is the operative temperature, in degrees Celsius (equal to the air temperature, t , for most measuring conditions
o a
in climatic chambers).
2.2
water vapour resistance
evaporative resistance
R
e
resistance to water vapour transfer between two surfaces, expressed in square metres kilopascal per watt
NOTE 1 In this International Standard it is considered as the equivalent uniform vapour resistance. This is the
resistance that, when uniformly covering the whole body surface (including hands, face, etc.), would result in the same
heat loss through evaporation as the actual, possibly non-uniform, vapour resistance. This resistance is the quotient of the
vapour pressure gradient between the surfaces (the driving force) over the evaporative heat loss per unit of body surface
area:
vapour pressure gradient
R = (9)
e
evaporative heat loss per unit of body surface area
NOTE 2 Similarly to heat resistance, it is divided into specific layers.
4 © ISO 2007 – All rights reserved

ISO 9920:2007(E)
2.2.1
total water vapour resistance
R
e,T
vapour resistance from the body surface to the environment (including all clothing, enclosed air layers and
boundary air layers) under reference conditions, static
2.2.2
basic water vapour resistance
R
e,cl
vapour resistance from the body surface to the outer clothing surface (including enclosed air layers) under
reference conditions, static
2.2.3
air water vapour resistance
R
e,a
vapour resistance of the boundary (surface) air layer around the outer clothing or, when nude, around the skin
surface
NOTE In analogy to heat resistance:
R
e,a
RR=+ (10)
e,T e,cl
f
cl
2.2.4
resultant total water vapour resistance
dynamic total water vapour resistance
R
e,T,r
vapour resistance from the body surface to the environment (including all clothing, enclosed air layers and
boundary air layers) under given environmental conditions and activities
NOTE 1 It is the total water vapour resistance (R ) value in actual situations (as opposed to reference conditions),
e,T
including the effects of movements and wind.
−1
NOTE 2 Values of R are defined for standardized conditions (static body, wind still, i.e. speed < 0,2 m ⋅ s ). When air
e,T
movement is present, or when the body moves, this will affect the vapour resistance (typically lowering it), in which case it
is referred to as the resultant or dynamic total water vapour resistance.
2.2.5
resultant basic water vapour resistance
dynamic basic water vapour resistance
R
e,cl,r
vapour resistance from the body surface to the outer clothing surface (including enclosed air layers) under
given environmental conditions and activities
NOTE 1 It is the basic water vapour resistance (R ) value in actual situations (as opposed to reference conditions),
e,cl
including the effects of movements and wind.
−1
NOTE 2 Values of R are defined for standardized conditions (static body, wind still, i.e. speed < 0,2 m ⋅ s ). When
e,cl
air movement is present, or when the body moves, this will affect the vapour resistance (typically lowering it), in which
case it is referred to as the resultant or dynamic basic water vapour resistance.
3 Application of this International Standard
Where possible, the insulation and vapour resistance values of a clothing ensemble should be measured
using equipment such as thermal (wetted or sweating) manikins, or by performing experiments involving
human subjects. Test procedures for the measurement of heat and vapour resistance are outlined in
Annexes D and E. However, given the cost and the need for specialized equipment, actual measurement will
most likely be beyond the reach of most users of this International Standard. In that case, the insulation and
vapour resistance shall be estimated using the methods specified in the following clauses and Annexes A, B
and C.
ISO 9920:2007(E)
For guidance, the stepwise approach is schematically represented in the flowcharts of Figure 2, for the
determination of heat resistance, and Figure 3, for the determination of vapour resistance. The various options
are described.
Figure 2 — Determining clothing insulation
6 © ISO 2007 – All rights reserved

ISO 9920:2007(E)
Figure 3 — Determining clothing vapour resistance
4 Estimation of thermal insulation of clothing ensemble based on tables and with
values measured on a standing thermal manikin
4.1 General
Tables in this International Standard provide data on the insulation of complete clothing ensembles, as well as
insulation values for individual garments that can be added to create complete ensembles. It is advisable to
use the tables of complete ensembles to match the actual ensemble, as this will provide a more accurate
value for clothing insulation than the summation of individual garments. Interpolation between the thermal
insulation of two ensembles may be used and, when an ensemble is found similar to the actual ensemble,
small corrections may also be made by adding or subtracting individual garment insulations to achieve the
best estimate of the insulation of the actual ensemble. Finally, corrections for movement and air velocity shall
be applied.
ISO 9920:2007(E)
4.2 Insulation values of complete ensembles
In Annex A, I and I values are listed for a selection of clothing ensembles. All of the values were measured
T cl
−1
on a static, standing, thermal manikin in low air movement (< 0,2 m ⋅ s ). In Table A.1, a short description of
the clothing ensembles is given. Tables A.2 to A.10 present more extended lists that can be used for finding a
clothing ensemble that is comparable with the actual clothing ensemble; f values are also given. The total
cl
clothing mass, where this is given, is based on garments that fit a standard person (European male size 52)
and does not include shoes. A number following the listing in the tables of individual garments making up most
of the ensembles refers to Annex B, where a more detailed description of the individual garment is presented,
including figures.
Annex A can also be used to select clothing for a workplace when the required insulation is known.
4.3 Ensemble thermal insulation values based on individual garments
Instead of using the ensembles in Annex A, the insulation for an ensemble, I , expressed in clo, may also be
cl
estimated, based on a summation of the insulation of individual garments using the following empirical
[31], [36]
equation :
I=+0,161 0,835 I (11)
cl ∑ clu
expressed in clo.
[32], [37]
Or, with slightly reduced accuracy :
I = I (12)
cl ∑ clu
expressed in square metres Kelvin per watt, or clo, and where I is the effective thermal insulation of the
clu
individual garments making up the ensemble, in values of either square metres Kelvin per watt or clo.
Such values are listed in Annex B.
The design of the various garments in Annex B is indicated by a type number, referring to drawings showing a
person dressed in various garment designs (Figures B.1 to B.14).
In some cases, the fabrics used are also listed. The type of material, however, has a limited influence on the
thermal insulation. Instead, the insulation is mainly influenced by the thickness (indicated in Annex B) and the
body surface area covered (indicated on the drawings).
It should be noted that the summations presented in Equations (11) and (12) are based on data with rather
uniform insulation distributions over the body. Such summations should not be used for extreme situations
(e.g. three layers on lower body and only a thin layer on upper body). The accuracy of the summation was
acceptable when actually measured data for the respective garments were used. When the separate
garments’ insulations were obtained from the tables, the accuracy of the summation was limited. Hence, it is
preferable to work with values of full ensembles (see Annex A).
The application range for which these relationships [Equations (11) and (12)] were tested is between 0,2 clo
and 1,6 clo.
4.4 Complete ensemble insulation corrected for small differences in composition
The accuracy of the summation of individual garments (4.3) is much less than that of matching the actual
ensemble with an ensemble taken from Annex A (4.2). Hence, when an exact match of the actual ensemble
with those of the tables of Annex A is not possible, but similar ensembles can be found, it is best to take the
similar ensemble insulation value and correct this for the difference in ensemble composition. For example, if
the actual ensemble has a different type of sweater, the ensemble insulation may be corrected for the
difference in insulation between the actual sweater and that of the sweater in the ensemble description of
8 © ISO 2007 – All rights reserved

ISO 9920:2007(E)
Annex A. For this purpose, the effective insulations of both clothing items are compared and the difference
used for adjustment of the ensemble value:
I =+II0,835×∆ (13)
cl,a cl,A clu
2 −1
with the result expressed in clo or in m⋅K⋅W , and where I is the basic insulation of the actual ensemble,
cl,a
I is the basic insulation of the ensemble according to Annex A, and ∆I is the correction for the difference
cl,A clu
in individual garments (negative for subtracting a garment or when replacing with a less insulative garment).
This can be the difference between two garments of the same type (replacing one sweater by another), or the
effective insulation of an extra garment, or a negative value in the case where the actual ensemble contains
one garment less. The I values are taken from Annex B.
clu
Corrections should be kept to a minimum, and interpolation between two relevant ensembles is preferred. In
adding and removing garments, it should be considered how the insulation is distributed. Adding a thin layer to
an already covered part of a cold weather ensemble will have minimal impact, compared with the large impact
of adding a thin layer to a nude part in such an ensemble.
4.5 Calculation of thermal insulation for clothing ensembles
As an alternative to the selection of an ensemble from the tables, it is also possible to determine the clothing
[32], [37]
insulation of an ensemble using the following empirically determined relationship :
Im=+0,919 0,255×− 0,008 74×A − 0,005 10×A (14)
cl COV,0 COV,1
where
I is the intrinsic clothing insulation, in clo;
cl
m is the clothing mass (without shoes), in kilograms;
A is the body surface area not covered by clothing, as a percentage of total body surface area;
COV,0
A is the body surface area covered by a single clothing layer, as a percentage of total body
COV,1
surface area.
In effect, Equation (14) assumes a certain multi-layer insulation for a given clothing mass and then subtracts
insulation for areas only covered with a single layer and for areas without clothing. The application range for
which this relation was tested is between 0,2 clo and 1,8 clo.
Guidance on how to calculate A is given in Annex H.
COV
4.6 Calculation of thermal insulation for individual garments
2 −1
The effective thermal insulation of an individual garment, I (m ⋅ K ⋅ W ), may also be estimated by
clu
IA=×0,00095 (15)
clu COV
or, if expressed in clo, using
IA=×0,0061 (16)
clu COV
where A is the body surface area covered by clothing (percentage of total skin area).
COV
The values for body surface area covered by clothing are shown for garments in the figures of Annex B.
[32]
Garment mass on its own is not a good predictor of garment insulation .
ISO 9920:2007(E)
When the thickness of the fabric used, d , expressed in metres, is also known, a more exact estimation of
fab
2 −1
I (m ⋅ K ⋅ W ) may be made using
clu
IA=+0,00067 0,217×d×A (17)
clu COV fab COV
or, if expressed in clo, using
IA=+0,0043 1,4×d×A (18)
clu COV fab COV
where d is the thickness of the fabric, in metres, measured in accordance with ASTM D1777 using a 7,5 cm
fab
−2
diameter pressure foot and 69,1 N ⋅ m pressure.
NOTE As the formula was derived using the ASTM method, no ISO alternative can be given, as this could affect the
relation.
The application range for which this relation [Equation (15)] was tested is between 0,02 clo and 0,5 clo or 5 %
to 82 % A . For Equation (17), the range was 0,02 clo to 1,05 clo.
COV
5 Estimation of clothing area factor
The outer surface area of a clothed person, A , is greater than the surface area of a nude body, A . The ratio
cl Du
of these is the clothing area factor, f [Equation (6)].
cl
[32], [45], [47]
The value of f is listed in Annex A for all clothing ensembles. It can be measured by photographic
cl
or whole body scanning methods. Pictures from different directions or whole body scans of the nude
person/manikin are compared with similar pictures/scans of the clothed person/manikin.
In view of the fact that the surface area increase depends on the clothing ensemble thickness, usually related
[32], [46], [48]
to its insulation, I , the clothing area factor may also be estimated from the following equations:
cl
2 −1
⎯ If I is expressed in square metres Kelvin per watt (m ⋅ K ⋅ W ):
cl
f=+1, 00 1, 81× I (19)
cl cl
⎯ If I is expressed in clo:
cl
f=+1,00 0,28× I (20)
cl cl
It should be noted that the correlation between f and I observed was low, so the estimate has limited
cl cl
[1]
reliability, especially for non-western clothing . Determination of f based on the table examples in Annex A,
cl
or, ideally, by actually measuring it, is therefore preferable, although in general the actual impact of f on the
cl
overall result for the insulation values is small. The application range for which these relations were tested is
between 0,2 clo and 1,7 clo.
6 Estimation of surface (or boundary) air layer insulation
In some cases, it is necessary to know the insulation of the surface air layer I (also called “boundary air
a
layer”) — for example, if I is known, but I is needed, or vice versa. In that case, Equation (7) may be used
T cl
with I and f , and either I or I as input.
a cl T cl
The static value of I ranges in most studies on which the tables in Annex A were based around 0,7 clo
a
2 −1 −1 −1
(0,109 m ⋅ K ⋅ W ) when measured at air velocities around 0,1 m ⋅ s to 0,15 m ⋅ s . Thus, for static
conditions, this value may be used as an estimate. For some cold weather clothing measurements the
−1
reference wind speed is set at 0,4 m ⋅ s ; see Reference [6].
10 © ISO 2007 – All rights reserved

ISO 9920:2007(E)
The insulation provided by the outer surface (boundary layer) thermal insulation (see Figure 1) is disturbed
[17]
when air movement increases or the person starts to move. The following correction equation shows by
−1
how much this reduction takes place, compared to the static, no-wind (v = 0,15 m ⋅ s ) I value taken
ar a
from Reference [11]:
⎡⎤
−×0,533 (vv− 0,15)+ 0,069× (− 0,15)− 0,462v+ 0,201v
ar ar w w
⎢⎥
⎣⎦
Ie=⋅I (21)
a,r a,static
where
I is the boundary layer thermal insulation, in clo;
a,r
−1 −1
v is the relative air velocity, in metres per second (minimum = 0,15 m ⋅ s ; maximum = 3,5 m ⋅ s );
ar
-1
v is the walking speed, in metres per second (maximum = 1,2 m ⋅ s );
w
I is the reference value for air insulation (= 0,7 clo).
a,static
Alternatively, I may be calculated as:
a
I = (22)
a
hh+
()
cr
where
h is the convective heat transfer coefficient, in watt per metre squared per degree Celsius
c
−2 −1
(W⋅m ⋅°C );
−2 −1
h is the radiative heat transfer coefficient, in watt per metre squared per degree Celsius (W⋅m ⋅°C ).
r
This does not include a correction for the effect of movement. The convective heat exchange coefficient, h ,
c
may be estimated as the greatest value from the following:
0,25
2,38 tt− (23)
sk a
3,5+ 5,2 v (24)
ar
0,6
8,7 v (25)
ar
The radiative heat exchange, h , may be estimated using:
r
A (tt+−273) (+ 273)
−8 r cl r
h=⋅5,67 10 ε× × (26)
r
At −t
DU cl r
The fraction of skin surface involved in heat exchange by radiation, A /A , is equal to 0,67 for a crouching
r DU
subject, 0,70 for a seated subject and 0,77 for a standing subject.
ISO 9920:2007(E)
7 Estimation of water vapour resistance
7.1 General
The water vapour resistance, R , of a clothing ensemble may be measured in experiments with subjects or
e,T
with a wetted or sweating thermal manikin. If this is not possible, R may be estimated using existing data, or
e,T
using a relationship between vapour and heat resistance to derive it from the latter.
7.2 Estimation of vapour resistance of clothing ensembles based on tables with values
measured on standing thermal manikin
In Annex C, R and R values are listed for a selection of clothing ensembles. All of the values were
e,T e,cl
−1
measured on a static, standing thermal manikin in low air movement (< 0,2 m ⋅ s ). A short description of the
clothing ensembles is given and the f values are also listed.
cl
A number following the listing in the tables of individual garments making up most of the ensembles refers to
Table C.5, where a detailed description of the garment fabric is presented.
7.3 Estimation of vapour resistance of clothing ensemble based on its relation with dry
heat resistance
2 −1
The total water vapour resistance, R , in square metre kilopascals per watt (m ⋅ kPa ⋅ W ) may be
e,T
estimated on the basis of the thermal insulation of that ensemble, I or I , by means of the permeability index,
T cl
−1
i , and the Lewis relation (L = 16,5 K ⋅ kPa ):
m
⎛⎞
I 0,06 I
a
T
R== + I (27)
⎜⎟
e,T cl
iL i f
mm cl
⎝⎠
2 −1
with I , I and I expressed in m ⋅ K ⋅ W .
T a cl
Typical values for i are given in Annex C, Table C.1. These are not as such related to the clothing’s
m
insulation, but to the permeability of the fabric layers. Based on the data for I and i , it is now possible to
T m
estimate R .
e,T
For an air layer, i as defined and used in Equation (27), is around 0,5. For impermeable garments that cover
m
the whole body including hands, feet and head it is close to zero. For many types of one- or two-layer,
permeable clothing, the permeability index, i , may be set to 0,38 and the equation for vapour resistance
m
2 −1
(m ⋅ kPa ⋅ W ) simplified to:
⎛⎞
I
a
R=×0,16II= 0,16 + (28)
⎜⎟
e,T T cl
f
cl
⎝⎠
For the clothing and air layer alone, similar relations apply:
0,06
R = (29)
e,a
f × h
cl c
I
cl
R=×0,06 (30)
e,cl
i
m,cl
where i is the permeability index for the clothing layer alone.
m,cl
For many permeable one- or two-layer clothing ensembles, i may be set to 0,34, giving:
m,cl
2 −1
R =×0,18 I  m ⋅ kP
...