Standard Test Methods for Textile Permeability — ASTM D737-18

Scope of application

1.1 This test method is used to measure the air permeability of textiles.

1.2 This test method is applicable to most fabrics, including woven fabrics, nonwoven fabrics, airbags with cloth, blankets, pile fabrics, knitted fabrics, pile fabrics, and multi-layer fabrics; fabrics can be unfinished, can also be heavy sizing, coating, resin finishing or by other finishing.

1.3 to the international system of units (SI expressed values are considered standard values, to inches – pounds units to indicate the approximate value.

1.4 This standard does not list all possible safety issues related to its use. The user of this standard shall be responsible for establishing appropriate safety and health practices prior to use and determining the scope of application.

1.5 This standard is revised in accordance with the internationally recognized principles for establishing standards, “Principles for the Preparation, Guidance and Recommended Practice of International Standards,” issued by the World Trade Organization Committee on Technical Trade Barriers.

Reference documents

2.1 ASTM standard

• D123 textile-related terms
• D1776 textile moisture conditioning and testing protocols
• D2904 Inter-laboratory textile comparison test procedure for obtaining normally distributed data (withdrawn in 2008)
• D2906 Specification for textile accuracy and deviation statements (withdrawn in 2008)
• D4850 Terminology related to fabric and fabric testing
• F778 Test method for breathability of filter media

 

Terminology

3.1 For the definition of textile-related terms involved in this method, such as breathability and fabric, see D4850.

3.2 For the terms used in this method, such as vertical production direction, production direction, and other textile terms, see D 123.

Overview of the test method

4.1 Air vertically through a known area of the fabric, adjust the pressure difference between the two sides of the fabric to a certain value, determine the flow rate of air, and determine the breathability of the fabric.

 

Meaning and function

5.1 The method can be used for acceptance testing of commercial deliveries. The current inter-laboratory accuracy estimate is acceptable and the test method is widely used for acceptance testing in trade.

5.1.1 If there are significant differences between the results of two or more laboratories, a comparison test should be performed to determine whether they are the same and whether there is statistical bias using appropriate statistical aids. At a minimum, ensure that this is as uniform as possible and from the same samples, then randomly distribute equal amounts to each laboratory for testing, and test results should be compared using statistical tests with unpaired data. If deviations are found, the cause should be found and corrected. Or adjust the test results in the future based on known deviations.

5.2 Breathability is a very important aspect of the performance of many textile materials, for example, air-filtering fabrics, airbag fabrics, taking fabrics, mosquito nets, parachutes, sails, tents, and vacuum cleaners. In the filtration process, for example, breathability is directly related to its effectiveness. Air permeability can also be used to characterize rainproof and breathable. The performance of fabrics such as ventilated breathable or plain coated is used to detect some changes in the production process.

5.3 Performance specifications are prepared based on breathability, both industrially and militarily, and are applied in fabric buying activities where breathability is of interest.

5.4 Structural factors as well as finishing techniques have a significant impact on breathability due to the altered length of the air pores in the fabric. Hot pressing finishes are often used for fabric flattening finishes but can reduce the breathability of the fabric. The air permeability of fabrics with different surface structures on the front and back side also differs when the airflow passes through from different directions.

5.4.1 For woven fabrics, yarn twist is also important. As the twist increases, the roundness and density of the yarn increase, so the yarn diameter and coverage factor decreases, the breathability increases, and the yarn flex and weave affect the shape and area of the spaces between the yarns, which may make the yarn easily elongated. Similar yarn elongation causes the fabric to open up and increase the void area, thereby increasing the amount of breathability.

5.4.2 An increase in yarn twist may also cause rounder, denser yarns to pack more tightly together in the woven fabric structure, thereby reducing breathability. For example, combed wada tweed may be less breathable than worsted tweed.

 

Instruments

6.1 Air permeability tester, including the following components.

6.1.1 Test head: round, test area 38.3 cm² (5.93 in.²) 0.3% soil

Note 1 ——Other test areas such as 5 cm² (0.75 in.²), 6.45 cm² (1.0 in.²), and 100 cm² (15.5 in.²) can also be substituted.

6.1.2 Fixed specimen clamping system: the pressure of at least 50 ± 5 N (11 ± 1 lbf), to prevent test head cross-formation and to minimize air leakage.

6.1.2.1 Reducing air leakage: Use a neoprene clamp ring of 55 Type A hardness, 20 mm (0.75 in.) wide and 3 mm (0.125 in.) thick, placed on both sides of the specimen.

Note 2——Since air leaks can affect test results, precautions must be taken, especially with heavy fabrics. The use of heavy rings and rubber gaskets on the clamping surface has been found to be beneficial in preventing air leakage. Test method F778 describes a series of clamping measures to prevent air leakage. Rubber gasket in some cases or after repeated use is easy to deform and will affect the test area should be used with caution, heavy ring for such as knitted fabrics or easy and test head against the fabric, is not suitable for heavy or stiff fabrics.

6.1.3 can obtain a stable airflow through the test area, and adjust the airflow rate so that the fabric under test on both sides of the device provides a minimum of 125Pa airflow pressure (12.7 mm water column or 0.5 inches of water column).

6.1.4 manometer or pressure gauge: connected to the test head below the specimen, used to test the airflow pressure drop through the specimen, expressed in Pa (mm water column into inches of water column) “accuracy tolerance of +2%.

6.1.5 flow meter: used to measure the airflow rate through the unit area fabric by measuring the volume or aperture, the unit with cm³/s/cm² (ft³/min/ft²), the accuracy tolerance of +2%.

6,1.6 Calibration disk or other means: known to its air permeability under a certain pressure difference, thus serving to verify the role of the equipment.

6.1.7 Methods of calculating and displaying the desired results, such as scale, digital display, and computer-driven systems.

6.2 Cutting template: Used to cut the specimen to size at least equal to the clamping area of the instrument (optional).

Sampling

7,1 Batch sample ——as a batch of acceptance test, according to the existing material specifications or other agreements between the buyer and suppliers, randomly selected a certain number of rolls or piles of specimens, and will be the basic sampling volume. If there is no agreement, take the number of rolls/pieces specified in Table 1.

NOTE 3——Appropriate specifications or agreements between supply and demand need to take into account variability between samples and variability between specimens of the same sample in order to propose a sampling plan that incorporates supply-side risk, buyer risk, acceptable quality levels, and ultimate quality levels.

Table 1 Number of rolls/rolls taken from the batch sample

Number of rolls/batches of specimens included in each batch of	Number of rolls/piles to be   included in the batch sample
1~3	All samples
4~24	4
25~50	5
Above 50	10% up to a maximum of 10 rolls/pi

7.2 Laboratory samples ——For the acceptability test, take a sample of the entire length along the length of each roll/pony from the batch sample, about 1m (1 yard) long. For each roll of test samples, take a sample from the middle, avoiding the beginning of each roll and the center portion of the roll.

7.3 Test Samples —— Unless otherwise agreed by the Seller and Buyer, from the laboratory sample, take 10 pieces of the sample, using the cut sample template described in 6.2. Or, if feasible, perform a breathability test without cutting the sample.

7.3.1 Sample cutting ——When cutting samples, the minimum size of the sample to be cut shall not be smaller than the clamping area and be well marked.

7.3.1.1 Sampling should be representative and distributed over a range of widths and lengths, preferably along diagonal diagonals, more than 1/10 of the width from the edge of the cloth. Ensure that the sample is not folded, has no creases, or folds, and avoids getting oil, water, grease, etc. when sampling.

 

Instrument preparation, calibration, and identification

8.1 The equipment setting procedure will be different for different manufacturers. Prepare and calibrate the instrument according to the instrument manual.

8.2 When a microprocessor automatic data acquisition system is used, set the appropriate parameters according to the instrument manual.

8.3 For the best results, place the instrument horizontally.

8.4 Perform verification checks according to your own laboratory requirements and in accordance with your own procedure manual to ensure that the machine is working properly.

8.4.1 Calibrate that the test range and differential pressure meet the requirements of the material to be tested.

Humidity adjustment

9.1 The specimen is pre-humidified under the pre-humidification standard atmosphere specified in D1776.

9.2 After pre-humidification, the test specimen is humidified to wet equilibrium under the standard atmosphere for testing specified in D 1776 or, if feasible, under the specific atmospheric conditions in which the test is actually performed.

9.3 If the permeability of the sample to be tested is known to be unaffected by heat or humidity, the specimen may be made without pre-humidification and conditioning according to the material specification or contractual agreement.

 

Operating procedures

10.1 Unless otherwise specified in the material specification or contract, place the moisture-adjusted test specimen in an environment with a standard atmospheric temperature of (21±1) °C, i.e., (70±2) °F, and relative humidity of (65±2) % for testing.

10.2 Handle the specimen carefully to avoid changing its natural state.

10.3 Place the specimen under the test head of the tester and start the test according to the operating instructions.

10.3.1 In the case of coated fabrics, place the fabric under the coating layer (towards the side with less pressure) to reduce air leakage.

10.4 Determine pressure differential according to the material description or contract requirements, or use 125 Pa (12.7 mm water column or 0.5 in. water column) if not otherwise specified.

10.5 Read and record independent test results and express them in the international system of units cm³/s/cm², or in ft³/min/ft², retaining 3 significant digits.

10.5.1 For specific requirements, the air leakage and the airflow through the specimen can be tested separately by covering the specimen with an impermeable cover to measure the air leakage and then subtracting it from the original test result to obtain effective air permeability.

10.6 Repeat steps 10.3-10.5 above to test 10 specimens in each laboratory.

10.6.1 If a 95% confidence interval is specified or contracted for, the number of specimens may be reduced, but at least 4 specimens must be tested.

 

Calculations

11.1 Air permeability, individual specimens —— Record the reading of each individual specimen tested in cm³/s/cm², or ft³/min/ft², retaining 3 significant digits. When calculating permeability results, follow the instrument instructions as needed.

Note 4 —— If the permeability results are measured above 600m (2000ft) above sea level, they need to be corrected according to the correction factor.

11.2 Permeability, mean —— Calculate the mean value of permeability

for each laboratory sample and batch sample.

11.3 Standard Deviation, Coefficient of Variation I —— Calculated when required.

11.4 Computer processing of data ——If computer processing of data is used, the calculations are usually included in the relevant software. It is recommended that computer data processing programs be validated with known data and that the software used to be described in the report.

Reporting

12.1 Report the standard method D 737 used for the breathability test, describing the specimen material and sampling method.

12.2 Report the following information in accordance with applicable material specifications or contract provisions:

12.2.1 Air permeability.

12.2.2 Report standard deviation and CV values, if calculated.

12.2.3 The pressure difference between the two sides of the specimen.

12.2.4 For microcomputer-processed data, describe the program (software) used.

12.2.5 Instrument Manufacturer and Model.

12.2.6 Any changes in the test method or instrumentation, including changes or additional gaskets.

 

Accuracy and Deviation

13.1 Summary —— In comparing two means, when the observed values are from the same trained operator, the same equipment is used, and test specimens are randomly selected on the same samples, then 95% of the time, the difference cannot exceed the single-person accuracies listed in Table 2 for the respective number of experiments, and Table 3 for those with similar mean values for the single-person precision. In any other case, a large variation is possible.

13.2 Woven fabrics, interlaboratory test data —— An interlaboratory test was conducted from 1994 to 1995 with three randomly selected specimens in each of the eight laboratories. Each laboratory was tested by two operators using this method on eight specimens of each sample, four on one day and four more on the next. Data were analyzed using specifications D 2904 and D 2906. The standard deviation was used to express the variance components of the air permeability and the results were calculated as shown in Table 3. The three woven fabric types were.

Material 5——S/2438, plain, oxford fabric, ring-spun

Material 6——S/0002H, plain, ring-spun

Material 7——S/28305, plain, continuous filament yarn

Table 2 Air permeability and critical difference A, ft³/min/ft²

Materials	Number of observations/average	Single person accuracy	Laboratory internal accuracy	Inter-laboratory accuracy
Woven fabrics
Plain, Oxford SpunYarn, Material 5	1	28.8	34.1	59.3
	2	20.3	27.4	55.7
	5	12.9	22.4	53.4
	10	9.1	20.5	52.6
Plain, short fiber Yarn, Material 6	1	9.7	13.0	30.4
	2	6.9	11.0	29.6
	5	4.3	9.6	29.1
	10	3.1	9.1	29.0
Plain, Continuous Filament Yarn, Material 7	1	2.8	2.8	4.4
	2	2.0	2.0	3.8
	5	1.3	1.3	3.5
	10	0.9	0.9	3.4
Nonwovens
Spunlace Nonwovens	1	27.6	33.9	52.0
	2	19.5	27.7	48.2
	5	12.3	23.3	45.8
	10	8.7	21.6	45.0
Dry Nonwovens	1	51.3	55.6	73.4
	2	36.3	42.1	63.8
	5	23.0	31.3	57.2
	10	16.2	26.8	54.9
Meltblown Nonwovens	1	8.8	9.3	21.5
	2	6.2	6.9	20.6
	5	4.0	4.9	20.0
	10	2.8	4.0	19.8
Needle punching nonwoven fabric	1	100.7	112.4	13.4
	2	71.2	87.0	88.2
	5	45.0	67.3	68.8
	10	31.8	59.2	61.0
Resin bonded nonwoven fabric	1	162.7	179.8	189.2
	2	115.1	138.1	150.1
	5	72.8	105.4	120.8
	10	51.5	92.0	109.3
Spunbond Nonwoven Fabric	1	234.6	234.6	251.2
	2	165.9	165.9	188.7
	5	104.9	104.9	138.1
	10	74.2	74.2	116.5
Hot Rolled Nonwoven Fabric	1	206.2	232.3	232.3
	2	145.8	180.8	180.8
	5	92.2	141.2	141.2
	10	65.2	125.2	125.2
Wet Nonwovens	1	1.34	2.80	3.24
	2	0.95	2.63	3.10
	5	0.60	2.52	3.01
	10	0.43	2.49	2.98

^Acritical difference is calculated based on infinite degrees of freedom using t = 1.960.

 

Table 3  Air permeability, ft³/min/ft²

Materials	Total average	Coefficient of variation expressed as standard deviationA
		Single person accuracy	Laboratory internal accuracy	Inter-laboratory accuracy
Woven fabrics
Plain, Oxford spun yarn, material 5	217.0	10.4	6.6	17.5
Plain, short fiber yarn, material 6	90.0	3.5	3.1	9.9
Plain, Continuous Filament yarn, material 7	8.3	1.0	0.0	1.2
Nonwovens
Spunlace Nonwovens	220.0	9.9	7.1	14.2
Dry Nonwovens	402.0	18.5	7.7	17.3
Meltblown Nonwovens	72.7	3.2	1.0	7.0
Needle punching	278.0	36.0	18.0	5.3
nonwoven fabric
Spunbond Nonwoven	474.0	84.6	0.0	32.4
Fabric Hot Rolled Nonwoven Fabric	564.0	74.4	38.6	0.0
Wet Nonwovens	17.2	0.5	0.9	0.6

^AThe square root of the variance component is used as the appropriate unit of measure for expressing variance performance, rather than the square of the variance.

 

13.3 Nonwovens, Interlaboratory Test Data – An interlaboratory test was conducted in 1994 in which eight samples were randomly selected for testing and eight specimens of each sample were tested by two operators per laboratory using this method, four on one day and four more on the next day. Data were analyzed using specifications D2904 and D 2906. The standard variance was used to express the variance components of the permeability, and the results were calculated as shown in Table 3.

The types of the eight samples and the number of participating laboratories were as follows:

Nonwoven materials	Number of participating laboratories
Hydroentanglement	5
Dry method	5
Meltblown method	5
Acupuncture	5
Resin bonding method	2
Spunbonding method	4
Hot rolling method	4

13.4 Precision—For the variance compositions reported in Table 3, two means of the observed values are considered significantly different at the 95% probability level if the deviations equal or exceed the critical deviations listed in Table 2. A sufficiently large deviation related to fabric type and structure exists to explain the variance composition and critical deviation, respectively. Therefore, no composite fabrics were compared.

Note 5—The critical deviation values listed in the table are all agreed-upon evaluations, especially those related to inter-laboratory measurement accuracy cuts. If possible, test data from the same number of random samples randomly assigned to each laboratory, which are of the same type of material with almost identical properties, should be compared one by one before a reasonable evaluation of the data deviations between the two laboratories is made.

Note 6 —The inter-laboratory test for resin-bonded nonwovens has only two laboratories, while the inter-laboratory test for thermocompression-bonded nonwovens and bonded nonwovens has only four laboratories, so there is a reasonable deviation from the inter-laboratory accuracy evaluation, which is low or high, and should therefore be used with caution.

13.5 Deviation—The air permeability value is limited to this experimental method only. In this range, the deviation of this experimental method is unknown.

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