ASTM C168-24
(Terminology)Standard Terminology Relating to Thermal Insulation
Standard Terminology Relating to Thermal Insulation
SCOPE
1.1 This standard provides definitions, symbols, units, and abbreviations of terms used in ASTM standards pertaining to thermal insulating materials, and to materials associated with them.
1.2 This terminology is not intended to be used to classify insulation materials as having particular properties. Rather, classification of insulation materials is to be done by the material standards themselves.
1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.
1.4 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
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This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: C168 − 24
Standard Terminology Relating to
1
Thermal Insulation
This standard is issued under the fixed designation C168; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope absorptance, n—the ratio of the radiant flux absorbed by a
body to that incident upon it.
1.1 This standard provides definitions, symbols, units, and
abbreviations of terms used in ASTM standards pertaining to
absorption, n—transformation of radiant energy to a different
thermal insulating materials, and to materials associated with
form of energy by interaction with matter.
them.
apparent thermal conductivity, λ , k , n—a thermal conduc-
a a
1.2 This terminology is not intended to be used to classify
tivity assigned to a material that exhibits thermal transmis-
insulation materials as having particular properties. Rather,
sion by several modes of heat transfer resulting in property
classification of insulation materials is to be done by the
variation with specimen thickness, or surface emittance. See
material standards themselves.
conductivity, thermal.
DISCUSSION—Thermal conductivity and resistivity are normally con-
1.3 This standard does not purport to address all of the
sidered to be intrinsic or specific properties of materials and, as such,
safety concerns, if any, associated with its use. It is the
should be independent of thickness. When nonconductive modes of
responsibility of the user of this standard to establish appro-
heat transfer are present within the specimen (radiation, free convec-
priate safety, health, and environmental practices and deter-
tion) this may not be the case. To indicate the possible presence of this
mine the applicability of regulatory limitations prior to use.
phenomena (for example, thickness effect) the modifier “apparent” is
1.4 This international standard was developed in accor-
used, as in apparent thermal conductivity.
dance with internationally recognized principles on standard-
DISCUSSION—Test data using the “apparent” modifier must be quoted
ization established in the Decision on Principles for the
only for the conditions of the measurement. Values of thermal conduc-
Development of International Standards, Guides and Recom-
tance (material C) and thermal resistance (material R) calculated from
mendations issued by the World Trade Organization Technical apparent thermal conductivity or resistivity, are valid only for the same
conditions.
Barriers to Trade (TBT) Committee.
DISCUSSION—Test data labeled with “apparent” shall not include any
2. Referenced Documents
equipment related measurement errors induced due to measurement
2
2.1 ASTM Standards:
attempts beyond an apparatus range or calibration.
D3574 Test Methods for Flexible Cellular Materials—Slab,
DISCUSSION—Use of the “apparent” modifier with system C or system
Bonded, and Molded Urethane Foams
R measurements is not permitted.
E456 Terminology Relating to Quality and Statistics
apparent thermal resistivity, r , n—a thermal resistivity
E2282 Guide for Defining the Test Result of a Test Method a
assigned to a material that exhibits thermal transmission by
2.2 ISO Standard:
several modes of heat transfer resulting in property variation
ISO 7345 Thermal Insulation—Physical Quantities and
3
with specimen thickness, or surface emittance. See
Definitions
resistivity, thermal.
3. Terminology
DISCUSSION—See entire discussion under apparent thermal conduc-
tivity.
3.1 Definitions:
area weight, n—weight per unit area for a specified sample, in
2 2
1
This terminology is under the jurisdiction of ASTM Committee C16 on units of lb/ft (kg/m ).
Thermal Insulation and is the direct responsibility of Subcommittee C16.94 on
Terminology. aerogel, n—a homogeneous, low-density solid phase material
Current edition approved April 15, 2024. Published April 2024. Originally
derived from a gel, in which the liquid component of the gel
approved in 1941. Last previous edition approved in 2022 as C168 – 22.
has been replaced with a gas.
DOI:101520/C0168-24.
2 DISCUSSION—The resulting material has a porous structure with an
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
average pore size below the mean free path of air molecules at standard
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Standards volume information, refer to the standard’s Document Summary page on atmospheric pressure and temperature.
the ASTM website.
3 batt, n—blanket insulatio
...
This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: C168 − 22 C168 − 24
Standard Terminology Relating to
1
Thermal Insulation
This standard is issued under the fixed designation C168; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope
1.1 This standard provides definitions, symbols, units, and abbreviations of terms used in ASTM standards pertaining to thermal
insulating materials, and to materials associated with them.
1.2 This terminology is not intended to be used to classify insulation materials as having particular properties. Rather,
classification of insulation materials is to be done by the material standards themselves.
1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility
of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of
regulatory limitations prior to use.
1.4 This international standard was developed in accordance with internationally recognized principles on standardization
established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued
by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
2. Referenced Documents
2
2.1 ASTM Standards:
D3574 Test Methods for Flexible Cellular Materials—Slab, Bonded, and Molded Urethane Foams
E456 Terminology Relating to Quality and Statistics
E2282 Guide for Defining the Test Result of a Test Method
2.2 ISO Standard:
3
ISO 7345 Thermal Insulation—Physical Quantities and Definitions
3. Terminology
3.1 Definitions:
absorptance, n—the ratio of the radiant flux absorbed by a body to that incident upon it.
absorption, n—transformation of radiant energy to a different form of energy by interaction with matter.
apparent thermal conductivity, λ ,k ,n—a thermal conductivity assigned to a material that exhibits thermal transmission by
a a
several modes of heat transfer resulting in property variation with specimen thickness, or surface emittance. See conductivity,
thermal.
1
This terminology is under the jurisdiction of ASTM Committee C16 on Thermal Insulation and is the direct responsibility of Subcommittee C16.94 on Terminology.
Current edition approved May 1, 2022April 15, 2024. Published May 2022April 2024. Originally approved in 1941. Last previous edition approved in 20192022 as
C168 – 19.C168 – 22. DOI:101520DOI:101520/C0168-24.⁄C0168-22.
2
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
3
Available from American National Standards Institute (ANSI), 25 W. 43rd St., 4th Floor, New York, NY 10036, http://www.ansi.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
1
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C168 − 24
DISCUSSION—
Thermal conductivity and resistivity are normally considered to be intrinsic or specific properties of materials and, as such, should be independent of
thickness. When nonconductive modes of heat transfer are present within the specimen (radiation, free convection) this may not be the case. To indicate
the possible presence of this phenomena (for example, thickness effect) the modifier “apparent” is used, as in apparent thermal conductivity.
DISCUSSION—
Test data using the “apparent” modifier must be quoted only for the conditions of the measurement. Values of thermal conductance (material C) and
thermal resistance (material R) calculated from apparent thermal conductivity or resistivity, are valid only for the same conditions.
DISCUSSION—
Test data labeled with “apparent” shall not include any equipment related measurement errors induced due to measurement attempts beyond an
apparatus range or calibration.
DISCUSSION—
Use of the “apparent” modifier with system C or system R measurements is not permitted.
apparent thermal resistivity, r ,n—a thermal resistivity assigned to a material that exhibits thermal transmission by several
a
modes of heat transfer resulting in property variation with specimen thickness, or surface emittance. See resistivity, thermal.
DISCUSSION—
See entire discussi
...
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