The Evaluation of Moisture Permeation Through Waterproof

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A Study on the Measurement of Water Vapor Transmission of Waterproof and
Breathable Fabrics, and the Wearing Test for Overcoats

G. T. Jou, Y.W. Lin, R. H. Gao, C.H. Huang
Department of Testing and Evaluation, China Textile Institute,
6, Chen –Tian Road, Tu-Chen City Taipei Shien, Taiwan, R.O.C

Abstract
The most common test methods used to measure moisture transmission of waterproof and
breathable fabrics currently are ASTM E96, JIS L 1099, ISO 11092 and BS 7209. To understand the
effect of water vapor transmission on the physiological comfort of overcoats made from these
waterproof and breathable fabrics, three wear trials in the resting, exercising and rainfall conditions
were conducted in this study.
The experiment proceeded in a climatic chamber at an ambient temperature 20℃, a relative
humidity 35%, and approximately an air velocity of 0.4m/s. The humidity in the microclimate was
taken as an index of moisture accumulation. Moreover, we examined the interaction between the
wear trials and the test methods of measuring water vapor transmission by means of statistical
correlation.
The experimental results show that, in the insensible metabolic heat condition i.e. resting
condition, people wearing any overcoat made from the waterproof and breathable fabrics tend to be
in the range of thermal physiological comfort. However, in exercising condition the overcoat made
from higher vapor permeability of fabrics has faster speed down to the region of comfortable area in
terms of the microclimatic humidity.
As far as the result of the correlation between the test methods for measuring moisture
permeability and the wearing test of human body, ASTM inverted cup method was found to be the
least relevant to the wearing test.

1. Introduction
In a rainy day, the required properties of overcoats for human body are considered to avoid
from the intrusion of rainwater, but to allow sweat evaporation. This requirement is noted for the
performance of waterproof and moisture permeability. The theory of waterproof is that, if the
diameter of porosity on fabric surface is smaller than that of raindrop, of which diameter is between
100 ~ 30000μm, the raindrop cannot pass through the overcoat. In terms of moisture permeability,
there are two different theories to explain the phenomenon. One is the formation of micro porous, of
which the diameter is larger than that of steam about 0.0004μm, on the surface of fabric (Figure 1).
Passing through the porous, the sweat vapor evaporated from our body can dissipate through fabric
to ambient environment. The other is the formation of hydrophilic membrane on the fabric surface
(Figure 2). Water or moisture accumulated in our body surface can utilize the ways of absorption,
diffusion, and evaporation through the membrane and leaves for ambient environment.[1] In order

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to investigate, under practical condition, the performance of the overcoats with different materials
claimed to be waterproof and moisture permeable, six kinds of overcoats were chosen to carry out
the test. These six overcoats were produced from the fabrics which had different coating and
lamination processes, consisting of one with PTFE micro porous membrane, three with PU micro
porous membrane but different thickness, one with non-porous PU hydrophilic membrane, and one
with normal PVC membrane. The humidity of microclimate near the skin was considered as the
major parameter in assessing the physiological comfort for these six overcoats on three wearing
conditions. The experimental results obtained from the wear tests and from fabric measurement by
different test methods for water vapor transmission, were compared to study the effect of using
different membranes on the performance of waterproof and moisture permeability.

2. Methods
2.1. Material
The basic properties of fabrics used to produce overcoats were described in Table 1.

Table 1 Basic Properties of the six overcoats
Code Material Lining Thickness (mm) Weight (g/m2)
PTFE PTFE micro porous + Null 0.51 218
Nylon fabric
PU1 PU micro porous + 100% Nylon mesh 0.23 156
Nylon fabric
PU2 PU micro porous + 100% Nylon mesh 0.28 158
Nylon fabric
PU3 PU micro porous + 100% Nylon mesh 0.25 128
Nylon fabric
HP Hydrophilic PU 100% Nylon mesh 0.30 147
non-porous film +
Nylon fabric
PVC PVC raincoat Null 0.20 188

2.2. Description of Testing Methods on Water vapor Permeability on Fabrics.
(1) JIS L1099 A1- Desiccant method
JIS desiccant method use a dish, where calcium chloride was put , under the condition of 40
℃ and 90% relative humidity, measuring the water vapor permeability.
Test Conditions：
(a) temperature：40±2℃
(b) humidity：90±5%R.H.
(c) air speed：0.8m/sec

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(d) test area (A)：cylinder with 6cm diameter
(e) moisture permeability＝(w2 －w1)/A
w1：the weight after putting in the set condition for one hour (g)
w2： the weight after putting in the set condition for one hour (g)
(2) JIS L 1099 A2－Water method
JIS water method measured the permeability by using a dish filled with water under the
condition of 40 ℃ and 50% relative humidity.
Test Conditions：
(a) Temperature：40±2℃
(b) relative humidity：50±5%R.H.
(c) air speed：0.8m/sec
(d) test area (A)：cylinder with 6cm diameter
(e) moisture permeability＝(w2 －w1)/A
w1：the weight after putting in the set condition for one hour.(g)
w2：the weight after putting in the set condition for two hours.(g)
ASTM E 96 B － Water method
The ASTM water method is similar to the JIS one. The only difference is the condition for
ASTM was set at 23 ℃(Figure 3).
Test Conditions：
(a) temperature：23±0.6℃
(b) relative humidity：50±2%R.H.
(c) air speed：2.8±0.25m/sec
(d) test area (A)：cylinder with 6.3cm diameter
(e) moisture permeability＝(w1 －w2)/A
w1： the weight after putting in the set condition for one hour (g)
w2： the weight after putting in the set condition for two hours (g)

(4) ASTM E 96 BW－Inverted cup method
The specialist method in ASTM is inverted water method. A dish filled with a certain amount
of water. After the mouth of dish is sealed by the fabric. The dish is inverted and put into a
condition of 23 ℃ and 50% relative humidity (Figure 4).
Test Conditions：
(a) temperature：23±0.6℃
(b) relative humidity：50±2%R.H.
(c ) air speed：2.80±0.25m/sec
(d) test area (A)：cylinder with 6.3cm diameter
(e) moisture permeability＝(w1 －w2)/A
w1：the weight after putting in the set condition for one hour (g)

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w2：the weight after putting in the set condition for two hours (g
ISO 11092 Skin model method
ISO skin model uses a 35℃ skin model plate under 35 ℃ and 40% R.H. to measure the
moisture permeability of fabric (Figure 5)
Test Conditions：(a) temperature：35±1℃
(b) air speed：1m/sec
(c) relative humidity：40±3%R.H.(d) test area：0.2×0.2m2
(e) moisture permeability
Pa

Ret  Tm

Pa ：water vapor pressure difference, ( Pa)
Ret：water vapor resistance, m2×Pa/W

T ：the latent heat of vaporization of water at Tm, about 0.672 W•h/g at 35 ℃
m

(6) Heated dish method
The heated dish method was invented by Mr. J.C. Gretton of Leeds University. The major
difference between this and the water method is the method utilizing the idea of temperature
gradient in measuring the moisture permeability (Figure 6).
Test conditions：
(a) temperature：20±1℃
(b) relative humidity：65±2%R.H.
(c) air speed：below 0.5 m/sec
(d) water temperature : 33℃
(e) .Test area (A)：cylinder with 8.3cm diameter
(f) .Moisture permeability＝(w1 －w2)/A
w1： the weight at the onset of the test (g)
w2：the weight after putting in the set condition for five hours.(g)

2.3. The techniques used to assess the physiological response of the overcoats in wearing
condition
The evaluation were carried out in the environment chamber controlled at the temperature
200.2℃ and the relative humidity 353% (Figure 7). A sensor, which measured the
humidity variance of the microclimate between skin and clothing, was put on the back of the
human body and SHINYEI TRH-DM3 recorder was utilized to record the measured reading
continuously.

2.4. Experimental procedure

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There were three different conditions for wearing test, i.e. resting condition, exercising
condition, and rainfall condition. Two subjects individually dressed in a clothing system,
which included cotton long-sleeve sportswear, slacks and the overcoats to be tested, and then
entered the chamber. The resting condition is defined as a person who sits in the chamber for
30 minutes (Figure 8). Exercising condition consists of three sessions, starting with 10
minutes of resting, followed by 10 minutes of jogging at the speed of 5.6 Km/hr, and then 20
minutes of resting (Figure 9). Rainfall condition begins with 10 minutes of resting, followed
by 20 minutes of exposure in a simulated rainfall of 120mm/hr, and then 20 minutes of resting
to recover his body to the original state (Figure 10,11). The physical data about the two
subjects participating in the test are listed on Table 2.

Table 2 Physical data about the physiology of the two subjects
Sex Height (cm) Weight (kg) Age
Person 1 Male 168 60 29
Person 2 Male 173 81 27

2.5. Moisture transmission with different test methods
We measured all the water vapor transmission of the six fabric specimens with different test
methods in order to understand the correlation between those standards and practical wearing
condition. The result of the measurement is shown on Table 3.

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Table 3 The result of moisture transmission with different test methods
Moisture ISO11092 JIS L1099 A-1 JIS L1099 A-2 ASTM E96 B ASTM E96 BW Water cup of
3
(g/m .24hr) method desiccant water method water method inverted water temperature
method method control
PU3 5448 6369 2832 1200 2448 5640
PTFE 5808 4128 2952 960 9370 5448
HP 4752 3118 1944 768 4445 4080
PU2 2400 2597 1920 648 834 2112
PU1 2184 1468 1104 432 382 1176
PVC 384 88 120 72 41 120

3. Results
3.1 Resting condition
The data plotted in Figure 12 describe the relationship between the average of microclimate
humidity and the length of the time at the resting condition. The curves illustrate that the
overcoats with moisture permeability, except PVC material, can adjust the microclimate
humidity into a lower humidity at the resting condition. Considering the microclimate
humidity at the 30th minute, the six overcoats follow the sequence as PU3, PTFE, HP, PU2,
PU1, PVC from the least to the largest.

50
REST
45
PTFE
Humidity(%)

40
PU1
35
PU2
30 PU3
HP
25
PVC
20

0 5 10 15 20 25 30
Time(min)

Fig.12：The microclimate humidity variance as a function of time at the resting condition

2. Exercising condition
The relationship between the means of the microclimate humidity and the time of the exercise
procedure for the six waterproof overcoat is indicated in Figure 13. The curve shows that, after a
10-minute jogging and a 20-minute recovery, the subjects follow the sequence as PU3, PTFE, HP,
PU2, PU1, and PVC according to the microclimate humidity from the least to the largest. The result
shows that the higher the moisture transmission, the larger the amount of moisture dissipates from

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the body moved to ambient environment. Consequently, the humidity of the microclimate for the
higher transmission fabric could decrease rapidly and reach a lower level of humidity.

100
REST JOGGING RECOVER
90 Y
80
Humidity(%)

70
PTFE
60 PU1
PU2
50
PU3
40
HP
30 PVC

20
0 5 10 15 20 25 30 35 40
Time(min)

Fig.13： The microclimate humidity variance as a function of time at exercising condition

3. Rainfall condition

60 PTFE
PU1
Humidity(%)

50 PU2
PU3
40
HP
30 PVC

20 REST RAINFALL RECOVER
Y
0 5 10 15 20 25 30 35 40 45 50
Time(min)

Fig. 14： The microclimate humidity variance as a function of time at rainfall condition

Figure 14 presents the microclimate humidity as a function of the testing time. The curve
shows that, since the rainfall begins, the humidity of the microclimate tends to increase without
falling. After a 20-minute exposure in the rainfall, according to the mount of the microclimate
humidity, the six overcoats follow the order form the least to the largest as HP, PU3, PU2, PTFE,
PU1, PVC. The test result also shows the tendency that the higher the water vapor transmission of
the fabric, the more the microclimate humidity is. This tendency is exactly opposite to the result

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derived from the resting and exercising conditions, which is that the higher the transmission ability,
the lower the humidity was. This was caused by the reason that during the rainfall testing condition,
the skin temperature of the subject is in the range of 32-33℃ and the humidity of the microclimate
is in the range of 30-45%. As a result, on the position near the skin, the amount of vapor is about
10.2-16.1 g/m3. However, at the temperature 20℃ and the humidity nearly 100% R.H., the
amount of vapor is about 17.3 g/m3 in the chamber of rainfall condition. It is generally accepted that
the evaporation passes through a clothing system and moves to inside of clothing by dissipation.
This leads to the fact that, given the moisture transmission of the fabric is higher, the microclimate
humidity becomes higher due to that vapor is normally easier to pass through the fabric. During
raining, the vapor easily passes through the permeable fabric. The humidity of the microclimate
closes to the skin still maintain at the level below 65% after 30 minutes in the session.

4. The correlation between the humidity of the microclimate and moisture transmission

Table 4 Correlation between different wearing states and the test standards
Moisture ISO11092 JIS L1099 A-1 JIS L1099 A-2 ASTM E96 B ASTM E96 BW Water cup of
3
(g/m .24hr) method desiccant water method water method inverted cup temperature
method method control
th
30 min. of rest -0.75 -0.85 -0.82 -0.88 -0.27 -0.75
con.
20th min. of -0.76 -0.93 -0.77 -0.87 -0.34 -0.81
exercise con.
40th min. of -0.88 -0.99 -0.95 -0.99 -0.51 -0.92
exercise con.
30th min. of 0.7 0.73 0.64 0.74 0.29 0.72
rainfall con.
50th min. of -0.38 -0.63 -0.53 -0.54 -0.23 -0.48
rainfall con.

Table 4 demonstrates that the correlation between the moisture transmissions measured by
different test standards and the microclimate humidity at different conditions. According to the
result of the correlation on Table 4, it is observed that the least correlation with any of different
wearing conditions that the transmission was measured by ASTM E96 BW method. In the exercise
condition, most of the test standards concerning moisture transmission appear to have a good
negative correlation with the microclimate humidity. At the point of 40 th minute of exercising
condition, the correlation from the highest to the lowest follows the sequence as ASTM water
method(r= -0.99), JIS desiccants method (r = -0.99), JIS water method (r = -0.95), water cup of
temperature control (r = -0.92), skin model (r = -0.88). Consequently, the result measured by most

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of the test standards is assumed to be perfectly response to the microclimate of the human body
after exercising. In terms of rest condition, the correlation to be in the range from –0.75 to –0.88
was a little worse than the result of the exercising condition. With reference to the rainfall condition,
the result of the microclimate humidity at 30th minute, where the simulated rain stopped, was only
some positive correlation with the results of these standard tests. The correlation from the highest to
the lowest is in the order of ASTM water method (r = 0.74), JIS desiccants method (r = 0.73), water
cup of temperature control (r = 0.72), skin model (0.70), and JIS water method (r = 0.64). However,
if considered at 50th minute, the correlation between wearing test and these standards become
significantly low because the wetting state on the fabric surface took place. This situation affects the
capability of the moisture permeability for these six overcoats.

Conclusion
According to the result of evaluating the performance of waterproof and moisture
permeability by human body wearing test, the following observations could be summed up as our
conclusion:
1. In the resting condition where the metabolic rate of human body was under the state of
insensible evaporation loss, those who wore the waterproof overcoat with the function of
moisture permeability could be in the range of physiological comfort. If wearing the waterproof
overcoat without moisture permeability function, after a period of time, the person might feel
muggy because of moisture and heat gathering inside the clothes.
2. In the exercising condition, the human body sweats in the exercising procedure. After this
procedure, those who wear the waterproof overcoat with higher moisture permeability felt
comfortable because the moisture inside the clothes immediately decreased to the acceptable
level. With reference to the humidity of the microclimate at 20th minute after exercising
procedure, In this paper, the six overcoats, followed the sequence, from the highest to lowest, as
PU3, PTFE, HP, PU2, PU1, PVC.
3. In the rainfall condition, if the human body does not work or take any activity, the amount of
vapor in ambient environment is higher than that inside the clothes. Therefore, the vapor
transferred from ambient into the clothes. The higher the permeability of moisture, the easier the
vapor passes through the clothes. This status causes higher humidity in the microclimate near
skin, but the humidity does not reach beyond 65%.RH
4. With reference to the correlation between the wearing tests of different condition and the test
standards of moisture transmission, JIS desiccant method appears to have the highest correlation
with the wearing test.
5. At present, the test standards of moisture transmission are all considered in the circumstance
without rainfall. However, the performance of moisture permeability for some of waterproof
fabric varies with its wetness level. If the performance of waterproof and moisture transmission
is considered simultaneously, the simulation of rainfall in the test of moisture transmission is
required.

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Acknowledge
The authors would like to acknowledge the financial support from Science and Technology
Department of Industrial Technology, Ministry of Economic Affairs, Taiwan, Republic of China.

Reference
1. Gohlke, D. J., Gore-Tex Fabric for Chemical Protective Clothing, J. Coated Fabrics, 19:180-186
2. Gretton, J. C., Brook, D. B., Dyson, H. M., Harlock, S.C. 1996. A Correlation between Test
Methods Used to Measure Moisture Vapor Transmission through Fabrics, J. Coated. Fabrics,
25:301-310
3. Japanese Standard Association 1994, JIS L 1099, JIS Handbook, 490-492
4. American Society for Testing and Materials 1992, ASTM E96, Annual Book of ASTM
Standards, 398-405

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