ASTM E96/E96M-14

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: E96/E96M − 13 E96/E96M − 14
Standard Test Methods for
Water Vapor Transmission of Materials
This standard is issued under the fixed designation E96/E96M; 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.
This standard has been approved for use by agencies of the U.S. Department of Defense.
1. Scope
1.1 These test methods cover the determination of water vapor transmission (WVT) of materials through which the passage of
water vapor may be of importance, such as paper, plastic films, other sheet materials, fiberboards, gypsum and plaster products,
wood products, and plastics. The test methods are limited to specimens not over 1 ⁄4 in. [32 mm] in thickness except as provided
in Section 9. Two basic methods, the Desiccant Method and the Water Method, are provided for the measurement of permeance,
and two variations include service conditions with one side wetted and service conditions with low humidity on one side and high
humidity on the other. Agreement should not be expected between results obtained by different methods. The method should be
selected that more nearly approaches the conditions of use.
1.2 The values stated in either SI units or inch-pound units are to be regarded separately as standard. The values stated in each
system may not be exact equivalents; therefore, each system shall be used independently of the other. Combining values from the
two systems may result in non-conformance with the standard. However, derived results can be converted from one system to the
other using appropriate conversion factors (see Table 1).
1.3 This standard does not purport to address all of the safety problems, if any, associated with its use. It is the responsibility
of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory
limitations prior to use.
2. Referenced Documents
2.1 ASTM Standards:
C168 Terminology Relating to Thermal Insulation
E177 Practice for Use of the Terms Precision and Bias in ASTM Test Methods
D449 Specification for Asphalt Used in Dampproofing and Waterproofing
D2301 Specification for Vinyl Chloride Plastic Pressure-Sensitive Electrical Insulating Tape
These test methods are under the jurisdiction of ASTM Committee C16 on Thermal Insulation and are the direct responsibility of Subcommittee C16.33 on Insulation
Finishes and Moisture.
Current edition approved Nov. 1, 2013Oct. 15, 2014. Published December 2013January 2015. Originally approved in 1953. Last previous edition approved in 20122013
as E96– 12.– 13. DOI: 10.1520/E0096_E0096M-13.10.1520/E0096_E0096M-14.
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.
A,B
TABLE 1 Metric Units and Conversion Factors
To Obtain (for the
Multiply by
same test condition)
WVT
2 2
g/h·m 1.43 grains/h·ft
2 2
grains/h·ft 0.697 g/h·m
Permeance
2 7
g/Pa·s·m 1.75 × 10 1 Perm (inch-pound)
−8 2
1 Perm (inch-pound) 5.72 × 10 g/Pa·s·m
Permeability
g/Pa·s·m 6.88 × 10 1 Perm inch
−9
1 Perm inch 1.45 × 10 g/Pa·s·m
A
These units are used in the construction trade. Other units may be used in other
standards.
B
All conversions of mm Hg to Pa are made at a temperature of 0°C.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E96/E96M − 14
E691 Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method
3. Terminology
3.1 Definitions of terms used in this standard will be found in Terminology C168, from which the following is quoted:
“water vapor permeability—the time rate of water vapor transmission through unit area of flat material of unit thickness induced
by unit vapor pressure difference between two specific surfaces, under specified temperature and humidity conditions.
Discussion—Permeability is a property of a material, but the permeability of a body that performs like a material may be used.
Permeability is the arithmetic product of permeance and thickness.
water vapor permeance—the time rate of water vapor transmission through unit area of flat material or construction induced by
unit vapor pressure difference between two specific surfaces, under specified temperature and humidity conditions.
Discussion—Permeance is a performance evaluation and not a property of a material.
3.2 water vapor transmission rate—the steady water vapor flow in unit time through unit area of a body, normal to specific
parallel surfaces, under specific conditions of temperature and humidity at each surface.”
4. Summary of Test Methods
4.1 In the Desiccant Method the test specimen is sealed to the open mouth of a test dish containing a desiccant, and the assembly
placed in a controlled atmosphere. Periodic weighings determine the rate of water vapor movement through the specimen into the
desiccant.
4.2 In the Water Method, the dish contains distilled water, and the weighings determine the rate of vapor movement through
the specimen from the water to the controlled atmosphere. The vapor pressure difference is nominally the same in both methods
except in the variation, with extremes of humidity on opposite sides.
5. Significance and Use
5.1 The purpose of these tests is to obtain, by means of simple apparatus, reliable values of water vapor transfer through
permeable and semipermeable materials, expressed in suitable units. These values are for use in design, manufacture, and
marketing. A permeance value obtained under one set of test conditions may not indicate the value under a different set of
conditions. For this reason, the test conditions should be selected that most closely approach the conditions of use. While any set
of conditions may be used and those conditions reported, standard conditions that have been useful are shown in Appendix X1.
6. Apparatus
6.1 Test Dish—The test dish shall be of any noncorroding material, impermeable to water or water vapor. It may be of any shape.
Light weight is desirable. A large, shallow dish is preferred, but its size and weight are limited when an analytical balance is chosen
2 2
to detect small weight changes. The mouth of the dish shall be as large as practical and at least 4.65 in. [3000 mm ]. The desiccant
or water area shall be not less than the mouth area except if a grid is used, as provided in 12.1, its effective area shall not exceed
10 % of the mouth area. An external flange or ledge around the mouth, to which the specimen may be attached, is useful when
shrinking or warping occurs. When the specimen area is larger than the mouth area, this overlay upon the ledge is a source of error,
particularly for thick specimens. This overlay material should be masked as described in 10.1 so that the mouth area defines the
test area. The overlay material results in a positive error, indicating excessive water vapor transmission. The magnitude of the error
is a complex function of the thickness, ledge width, mouth area, and possibly the permeability. This error is discussed by Joy and
Wilson (1) (see 13.4.3). This type of error should be limited to about 10 to 12 %. For a thick specimen the ledge should not exceed
3 1
⁄4 in. [19 mm] for a 10-in. [254-mm] or larger mouth (square or circular) or ⁄8 in. [3 mm] for a 5-in. [127-mm] mouth (square
or circular). For a 3-in. [76-mm] mouth (square or circular) the ledge should not exceed 0.11 in. [2.8 mm] wide. An allowable ledge
may be interpolated for intermediate sizes or calculated according to Joy and Wilson.(1) A rim around the ledge (Fig. X2.1) may
be useful. If a rim is provided, it shall be not more than ⁄4 in. [6 mm] higher than the specimen as attached. Different depths may
be used for the Desiccant Method and Water Method, but a ⁄4-in. [19-mm] depth (below the mouth) is satisfactory for either
method.
6.2 Test Chamber—The room or cabinet where the assembled test dishes are to be placed shall have a controlled temperature
(see Note 1) and relative humidity. Some standard test conditions that have been useful are given in Appendix X1. The temperature
chosen shall be determined according to the desired application of the material to be tested (see Appendix X1). The relative
humidity shall be maintained at 50 6 2 %, except where extremes of humidities are desired, when the conditions shall be 100 6
1.8°F [38 6 1°C] and 90 6 2 % relative humidity. Both temperature and relative humidity shall be measured frequently or
preferably recorded continuously. Air shall be continuously circulated throughout the chamber, with a velocity sufficient to
maintain uniform conditions at all test locations. The air velocity over the specimen shall be between 0.066 and 1 ft/s [0.02 and
-1
0.3 m·s ]. Suitable racks shall be provided on which to place the test dishes within the test chamber.
The boldface numbers in parentheses refer to the list of references at the end of this standard.
The minimum acceptable is to perform this measurement each time the sample is weighed.
E96/E96M − 14
NOTE 1—Simple temperature control by heating alone is usually made possible at 90°F [32°C]. However, it is very desirable to enter the controlled
space, and a comfortable temperature is more satisfactory for that arrangement. Temperatures of 73.4°F [23°C] and 80°F [26.7°C] are in use and are
satisfactory for this purpose. With cyclic control, the average test temperature may be obtained from a sensitive thermometer in a mass of dry sand. The
temperature of the chamber walls facing a specimen over water should not be cooler than the water to avoid condensation on the test specimen.
6.3 Balance and Weights—The balance shall be sensitive to a change smaller than 1 % of the weight change during the period
when a steady state is considered to exist. The weights used shall be accurate to 1 % of the weight change during the steady-state
period (Note 2). A light wire sling may be substituted for the usual pan to accommodate a larger and heavier load.
6.4 Thickness-Measuring Gage—The nominal thickness of the specimen shall be determined using a thickness-measuring gage
with an accuracy of 61 % of the reading or 0.0001 in. [0.0025 mm], whichever is greater.
-1 -1 -2
NOTE 2—For example: 1-perm [57 ng·Pa ·s ·m ] specimen 10 in. [254 mm] square at 80°F [26.7°C] passes 8.6 grains or 0.56 g/day. In 18 days of
steady state, the transfer is 10 g. For this usage, the balance must have a sensitivity of 1 % of 10 g or 0.1 g and the weights must be accurate to 0.1 g.
If, however, the balance has a sensitivity of 0.2 g or the weights are no better than 0.2 g, the requirements of this paragraph can be met by continuing
the steady state for 36 days. An analytical balance that is much more sensitive will permit more rapid results on specimens below 1 perm [57
-1 -1 -2
ng·Pa ·s ·m ] when the assembled dish is not excessively heavy.
7. Materials
7.1 Desiccant and Water:
7.1.1 For the Desiccant Method, anhydrous calcium chloride in the form of small lumps that will pass a No. 8 [2.36-mm] sieve,
and free of fines that will pass a No. 30 [600-μm] sieve, shall be used (Note 3). It shall be dried at 400°F [200°C] before use.
NOTE 3—If CaCl will react chemically on the specimen, an adsorbing desiccant such as silica gel, activated at 400°F [200°C], may be used; but the
moisture gain by this desiccant during the test must be limited to 4 %.
7.1.2 For the Water Method, distilled water shall be used in the test dish.
7.2 Sealant—The sealant used for attaching the specimen to the dish, in order to be suitable for this purpose, must be highly
resistant to the passage of water vapor (and water). It must not lose weight to, or gain weight from, the atmosphere in an amount,
over the required period of time, that would affect the test result by more than 2 %. It must not affect the vapor pressure in a
-2 -1 -1
water-filled dish. Molten asphalt or wax is required for permeance tests below 4 perms [230 ng·m · s ·Pa ]. Sealing methods are
discussed in Appendix X2.
8. Sampling
8.1 The material shall be sampled in accordance with standard methods of sampling applicable to the material under test. The
sample shall be of uniform thickness. If the material is of nonsymmetrical construction, the two faces shall be designated by
distinguishing marks (for example, on a one-side-coated sample, “I” for the coated side and “II” for the uncoated side).
9. Test Specimens
9.1 Test specimens shall be representative of the material tested. When a product is designed for use in only one position, three
specimens shall be tested by the same method with the vapor flow in the designated direction. When the sides of a product are
indistinguishable, three specimens shall be tested by the same method. When the sides of a product are different and either side
may face the vapor source, four specimens shall be tested by the same method, two being tested with the vapor flow in each
direction and so reported.
9.2 A slab, produced and used as a laminate (such as a foamed plastic with natural “skins”) may be tested in the thickness of
use. Alternatively, it may be sliced into two or more sheets, each being separately tested and so reported as provided in 9.4,
provided also, that the “overlay upon the cup ledge” (6.1) of any laminate shall not exceed ⁄8 in. [3 mm].
9.3 When the material as used has a pitted or textured surface, the tested thickness shall be that of use. When it is homogeneous,
however, a thinner slice of the slab may be tested as provided in 9.4.
9.4 In either case (9.2 or 9.3), the tested overall thickness, if less than that of use, shall be at least five times the sum of the
-2 -1 -1
maximum pit depths in both its faces, and its tested permeance shall be not greater than 5 perms [≈ 300 ng·m ·s ·Pa ].
9.5 For homogeneous (not laminated) materials with thickness greater than ⁄2 in., the overall nominal thickness of each
specimen shall be measured with an accuracy of 61 % of the reading at the center of each quadrant and the results averaged.
-2 -1 -1
9.6 When testing any material with a permeance less than 0.05 perms [3 ng·m ·s ·Pa ] or when testing a low permeance
material that may be expected to lose or gain weight throughout the test (because of evaporation or oxidation), it is strongly
recommended that an additional specimen, or “dummy,” be tested exactly like the others, except that no desiccant or water is put
in the dish. Failure to use this dummy specimen to establish modified dish weights may significantly increase the time required
to complete the test. Because time to reach equilibrium of water permeance increases as the square of thickness, thick, particularly
hygroscopic, materials may take as long as 60 days to reach equilibrium conditions.
E96/E96M − 14
10. Attachment of Specimen to Test Dish
10.1 Attach the specimen to the dish by sealing (and clamping if desired) in such a manner that the dish mouth defines the area
of the specimen exposed to the vapor pressure in the dish. If necessary, mask the specimen top surface, exposed to conditioned
air so that its exposure duplicates the mouth shape and size and is directly above it. A template is recommended for locating the
mask. Thoroughly seal the edges of the specimen to prevent the passage of vapor into, or out of, or around the specimen edges
or any portion thereof. The same assurance must apply to any part of the specimen faces outside their defined areas. Suggested
methods of attachment are described in Appendix X2.
NOTE 4—In order to minimize the risk of condensation on the interior surface of the sample when it is placed in the chamber, the temperature of the
water prior to preparation of the test specimen should be within 62°F [61°C] of the test condition.
11. Procedure for Desiccant Method
11.1 Fill the test dish with desiccant within ⁄4 in. [6 mm] of the specimen. Leave enough space so that shaking of the dish, which
must be done at each weighing, will mix the desiccant.
11.2 Attach the specimen to the dish (see 10.1) and place it in the controlled chamber, specimen up, weighing it at once. (This
weight may be helpful to an understanding of the initial moisture in the specimen.)
11.3 Weigh the dish assembly periodically, often enough to provide eight or ten data points during the test. A data point is the
weight at a particular time. The time that the weight is made should be recorded to a precision of approximately 1 % of the time
span between successive weighing. Thus, if weighings are made every hour, record the time to the nearest 30 s; if recordings are
made every day, a time to the nearest 15 min would be allowed. At first the weight may change rapidly; later a steady state will
be reached where the rate of change is substantially constant. Weighings should be accomplished without removal of the test dishes
from the controlled atmosphere, but if removal is prescribed necessary, the time the specimens are kept at different conditions,
temperature or relative humidity, or both, should be kept to a minimum. When results of water vapor transmission are expected
-2 -1 -1
to be less than 0.05 perm [3 ng·m ·s ·Pa ], a dummy specimen is strongly recommended. Such a dummy specimen should be
attached to an empty cup in the normal manner. The environmental effects of temperature variation and buoyancy variability due
to barometric pressure fluctuation can be arithmetically tared out of the weighing values. This precaution permits earlier and more
reliable achievement of equilibrium conditions. Analyze the results as prescribed in 13.1.
11.4 Terminate the test or change the desiccant before the water added to the desiccant exceeds 10 % of its starting weight. This
limit cannot be exactly determined and judgement is required. The desiccant gain may be more or less than the dish weight-gain
when the moisture content of the specimen has changed.
NOTE 5—The WVT of some materials (especially wood) may depend on the ambient relative humidity immediately before the test. An apparent
hysteresis results in higher WVT if the prior relative humidity was above the test condition and vice versa. It is therefore recommended that specimens
of wood and paper products be conditioned to constant weight in a 50 % relative humidity atmosphere before they are tested. Some specimens may be
advantageously preconditioned to minimize the moisture that the specimen will give up to the desiccant. This applies when the specimen is likely to have
high moisture content or when it is coated on the top (vapor source) side.
12. Procedure for Water Method
3 1
12.1 Fill the test dish with distilled water to a level ⁄4 6 ⁄4 in. [19 6 6 mm] from the specimen. The air space thus allowed
has a small vapor resistance, but it is necessary in order to reduce the risk of water touching the specimen when the dish is handled.
Such contact invalidates a test on some materials such as paper, wood, or other hygroscopic materials. The water depth shall be
not less than ⁄8 in. [3 mm] to ensure coverage of the dish bottom throughout the test. However, if the dish is of glass, its bottom
must be visibly covered at all times but no specific depth is required. Water surges may be reduced by placing a grid of light
noncorroding material in the dish to break the water surface. This grid shall be at least ⁄4 in. [6 mm] below the specimen, and it
shall not reduce the water surface by more than 10 %.
NOTE 6—For the Water Method, baking the empty dish and promptly coating its mouth with sealant before assembly is recommended. The water may
be added most conveniently after the specimen is attached, through a small sealable hole in the dish above the water line.
12.2 Attach the specimen to the dish (see 10.1). Some specimens are likely to warp and break the seal during the test. The risk
is reduced by preconditioning the specimen, and by clamping it to the dish ledge (if one is provided).
12.3 Weigh the dish assembly and place it in the controlled chamber on a true horizontal surface. Follow the procedure given
in 11.3. If the test specimen cannot tolerate condensation on the surface, the dish assembly shall not be exposed to a temperature
that differs by more than 5°F [3°C] from the control atmosphere to minimize the risk of condensation on the specimen. When
-2 -1 -1
results of water vapor transmission are expected to be less than 0.05 perm [3 ng·m ·s ·Pa ], a dummy specimen is strongly
recommended. Such a dummy specimen should be attached to an empty cup in the normal manner. The environment effects of
temperature variation and buoyancy variability due to barometric pressure fluctuation can be arithmetically tared out of the
weighing values. This precaution permits earlier and more reliable achievement of equilibrium conditions. Analyze the results as
prescribed in 13.1.
E96/E96M − 14
12.4 Where water is expected to be in contact with the barrier in service, proceed as in 11.3 except place the dish in an inverted
position. The dish must be sufficiently level so that water covers the inner surface of the specimen despite any distortion of the
specimen due to the weight of the water. With highly permeable specimens it is especially important to locate the test dish so that
air circulates over the exposed surface at the specified velocity. The test dishes may be placed on the balance in the upright position
for weighing, but the period during which the wetted surface of the specimen is not covered with water must be kept to a minimum.
13. Calculation and Analysis of Results
13.1 The results of the rate of water vapor transmission may be determined either graphically or numerically.
13.1.1 Dummy Specimen—If a dummy specimen has been used to compensate for variability in test conditions, due to
temperature or barometric pressure, or both, the daily recorded weights can be adjusted by calculating the weight change from
initial to time of weighing. This adjustment is made by reversing the direction of the dummy’s weight change, relative to its initial
weight, and modifying all the appropriate specimen weight(s) recorded at this time. This permits earlier achievement of
equilibrium conditions. An alternate procedure, particular for tests of long duration and more than six weighings, is to subtract the
arithmetic mean slope of the rate of weight change of the dummy specimen from the arithmetic mean slope of each similar
specimen to get an effective rate of weight change. These procedures are also desirable if the specimen is changing weight due
to a curing process while under test.
13.1.2 Graphic Analysis—Plot the weight, modified by the dummy specimen when used, against elapsed time, and inscribe a
curve that tends to become straight. Judgment here is required and numerous points are helpful. When a straight line adequately
fits the plot of at least six properly spaced points (periodic weight changes matching, or exceeding 20 % of the multiple of 100
times the scale sensitivity), a nominally steady state is assumed, and the slope of the straight line is the rate of water vapor
transmission.
13.1.3 Numerical Analysis—A mathematical least squares regression analysis of the weight, modified by the dummy specimen
when used, as a function of time will give the rate of water vapor transmission. An uncertainty, or standard deviation of this rate,
can also be calculated to define the confidence band. For very low permeability materials, this method can be used to determine
the results after 30 to 60 days when using an analytical balance, with a sensitivity of ≈1 mg, even if the weight change does not
meet the 100 times the sensitivity requirement of 6.3. These specimens must be clearly identified in the report.
13.2 Calculate the water vapor transmission, WVT, and permeance as follows:
13.2.1 Water Vapor Transmission:
WVT 5 G/tA 5 ~G/t!/A (1)
where:
In inch-pound units:
G = weight change, grains (from the straight line),
t = time during which G occurred, h,
G/t = slope of the straight line, grains/h,
A = test area (cup mouth area), ft , and
WVT = rate of water vapor transmission, grains/h·ft .
In metric units:
G = weight change (from the straight line), g,
t = time, h,
G/t = slope of the straight line, g/h,
A = test area (cup mouth area), m , and
WVT = rate of water vapor transmission, g/h·m .
13.2.2 Permeance:
Permeance 5 WVT/Δp 5 WVT/S~R 2 R ! (2)
1 2
where:
In inch-pound units:
Δp = vapor pressure difference, in. Hg,
S = saturation vapor pressure at test temperature, in. Hg,
R = relative humidity at the source expressed as a fraction (the test chamber for desiccant method; in the dish for water
method), and
R = relative humidity at the vapor sink expressed as a fraction.
In metric units:
Δp = vapor pressure difference, mm Hg (1.333 × 10 Pa),
S = saturation vapor pressure at test temperature, mm Hg (1.333 × 10 Pa),
E96/E96M − 14
R = relative humidity at the source expressed as a fraction (the test chamber for desiccant method; in the dish for water
method), and
R = relative humidity at the vapor sink expressed as a fraction.
13.2.3 In the controlled chamber the relative humidity and temperature are the average values actually measured during the test
and (unless continuously recorded) these measurements shall be made as frequently as the weight measurements. In the dish the
relative humidity is nominally 0 % for the desiccant and 100 % for the water. These values are usually within 3 % relative humidity
-1 -1 -2
of the actual relative humidity for specimens below 4 perms [230 ng·Pa ·s ·m ] when the required conditions are maintained (no
more than 10 % moisture in CaCl and no more than 1 in. [25 mm] air space above water).
13.3 The calculation of permeability is optional and can be done only when the test specimen is homogeneous (not laminated)
and not less than ⁄2 in. [12.5 mm] thick, calculate its average permeability as follows:
Average permeability 5 Permeance 3Thickness (3)
13.4 Corrections—It is important that all applicable corrections be made to all measurements that result in permeance value
-1 -1 -2 -1
more than 2-perm [114 ng·Pa ·s ·m ]. Corrections for materials with permeance value below 2-perm [114 ng·Pa ·
-1 -2
s ·m ] are insignificant and need not be done. The procedures for making various corrections, as summarized below, are found
in the literature. [2,3,4,5)
13.4.1 Buoyancy Correction—The duration for one set of measurements can be many days or weeks. The atmospheric pressure
may significantly change during such periods. If the test specimen is highly vapor resistant, the changes in mass due to vapor
transport may be overshadowed by the apparent gravimetric changes observed. In such cases, all gravimetric data should be
corrected to vacuum or any base line pressure. The following equation (2) can be used for buoyancy correction.
m ρ ρ 2 ρ
~ !
2 a 1 2
5 11 (4)
m ρ ~ρ 2 ρ !
1 1 2 a
where:
m = mass recorded by balance, kg,
m = mass after buoyancy correction, kg,
-3
ρ = density of air, kg m ,
a
-3
ρ = density of material of balance weights, kg m , and
-3
ρ = bulk density of test assembly, kg m .
13.4.1.1 The density of air can be calculated using the ideal gas law for the measured atmospheric pressure and ambient
temperature.
13.4.1.2 The buoyancy correction is important (6) when measured mass changes are in the range of 0 to 100 mg.
13.4.2 Corrections for Resistance due to Still Air and Specimen Surface—In general, if the material is highly permeable, these
corrections are more significant. With known thickness of the still air layer in the cup, the corresponding vapor resistance can be
calculated using the following equation(3) for permeability.
25 1.81
2.306 310 P T
o
δ 5 (5)
S D
a
R TP 273.15
v
where:
-1 -1 -1
δ = permeability of still air, kg·m ·s ·Pa ,
a
T = temperature, K,
P = ambient pressure, Pa,
P = standard atmospheric pressure, that is, 101325 Pa, and
o
-1 -1
R = ideal gas constant for water, that is, 461.5 J·K ·kg .
v
13.4.2.1 In the absence of any measured data, the surface resistances (that is, inside and outside surfaces of the specimen) may
be approximated using Lewis’ relation.(4) For cup methods that follow this standard, the total surface resistance (Hansen and Lund
7 2 -1
(5)) should be ≈ 4 × 10 Pa·s·m ·kg .
13.4.3 Edge Mask Correction—The following equation (Joy and Wilson(1)) is to be used to correct the excess WVT effect due
to edge masking:
400t 2
Percent excess WVT 5 log (6)
S D
e 2 2πb/t
~ !
πS 11e
where:
t = specimen thickness, m,
b = width of masked edge, m, and
S = four times the test area divided by the perimeter, m.
13.4.3.1 If the cup assembly includes any edge masking this correction shall be made.
E96/E96M − 14
FIG. 1
13.5 Metric units and conversion factor are given in Table 1.
13.6 Example (in SI unit)—In a desiccant test on a sample of medium density glass fiber insulation the following results were
recorded.
Thickness of the specimen = 25.81 mm
Test area = 0.01642 m
Mass of the test specimen = 20.44 g
Mass of the desiccant = 554.8 g
Initial mass of the test assembly = 1.257810 kg
Thickness of air layer in the cup = 15 mm
Mass of Barometric
Elapsed Change Chamber Chamber
the Test Pressure
Time in Mass Temperature RH
Assembly mm Hg
(h) (g) (°C) (% )
(g) (kPa)
0.000 1257.810 0.000 22.83 52.60 744.7
(99.27)
6.067 1259.469 1.659 22.84 52.6 741.11
(98.79)
26.633 1264.609 6.799 22.78 52.2 744.41
(99.23)
53.150 1271.062 13.252 22.82 52.1 743.21
(99.07)
143.767 1290.773 32.963 22.74 52.2 757.69
(101.00)
168.283 1296.389 38.579 22.78 52.1 749.81
(99.95)
192.883 1301.953 44.143 22.78 52.1 758.44
(101.10)
13.6.1 Buoyancy Correction—As mentioned in 13.4.1, the buoyancy effect will be insignificant for this set of readings as
recorded changes of mass are all above 100 mg. However, for example, the corrected mass of the test assembly weight 1257.810
st
g (1 reading) can be calculated using Eq 4.
-3
m = mass recorded by balance, kg = 1257.810 × 10 kg
P = Barometric pressure, Pa = 99.27 × 10 Pa
R = Gas constant for dry air = 287.055 J / (kg·K)
T = Chamber temperature = 22.83 + 273.15 = 295.98 K
-3 -3
ρ = density of air, kg m = P / (RT) = 1.1684 kg m
a
-3 -3
ρ = density of material of balance weights, kg m = 8000 kg m
-3
h = height of the test assembly, m = 44.7 × 10 m
-3
d = diameter of the test assembly, m = 168.0 × 10 m
-3
ρ = bulk density of test assembly, kg m
43m
5 51269.4 kg m
π3d 3h
1 1
-3
m = mass after buoyancy correction = 1258.78 × 10 kg
13.6.2 A graphic analysis of the data, according to 13.1.2 is shown in Fig. 1.
-1
13.6.3 A linear least-squares analysis of the data according to 13.1.3 gives the slope of the straight line as 0.225 6 0.002 g·h ,
with a linear regression coefficient > 0.998.
E96/E96M − 14
-1 2
WVT = 0.225 g·h ⁄ 0.01642 m
-1 -2 6 -2 -1
= 19.595 grains·h ·ft (' 3.81 × 10 ng·m ·s )
S = 2775.6 Pa
R = 0.523
R = 0
6 -2 -1
Permeance = 3.81 × 10 ng·m ·s ⁄ (2775.6 Pa × 0.523)
-2 -1 -1
= 2630 ng·m ·s ·Pa
13.6.4 Corrections for Resistance due to Still Air and Specimen Surface:
Permeability of still air layer (Eq 5)
25 1.81
2.306310 3101325 22.791273.15
5δ 5
S D
a
461.53 22.791273.15 399860 273.15
s d
-1 -1 -1
= 198 ng·m ·s
...