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: D737 − 04 (Reapproved 2016)
`
`Standard Test Method for
`Air Permeability of Textile Fabrics1
`
`This standard is issued under the fixed designation D737; 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 This test method covers the measurement of the air
`permeability of textile fabrics.
`1.2 This test method applies to most fabrics including
`woven fabrics, nonwoven fabrics, air bag fabrics, blankets,
`napped fabrics, knitted fabrics, layered fabrics, and pile fabrics.
`The fabrics may be untreated, heavily sized, coated, resin-
`treated, or otherwise treated.
`1.3 The values stated in SI units are to be regarded as the
`standard. The values stated in inch-pound units may be
`approximate.
`1.4 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 appro-
`priate safety and health practices and determine the applica-
`bility of regulatory limitations prior to use.
`
`2. Referenced Documents
`2.1 ASTM Standards:2
`D123 Terminology Relating to Textiles
`D1776 Practice for Conditioning and Testing Textiles
`D2904 Practice for Interlaboratory Testing of a Textile Test
`Method that Produces Normally Distributed Data (With-
`drawn 2008)3
`D2906 Practice for Statements on Precision and Bias for
`Textiles (Withdrawn 2008)3
`D4850 Terminology Relating to Fabrics and Fabric Test
`Methods
`F778 Methods for Gas Flow Resistance Testing of Filtration
`Media
`
`1 This test method is under the jurisdiction of ASTM Committee D13 on Textiles
`and is the direct responsibility of Subcommittee D13.59 on Fabric Test Methods,
`General.
`Current edition approved July 1, 2016. Published July 2016. Originally approved
`in 1943 . Last previous edition approved in 2012 as D737 – 04(2012). DOI:
`10.1520/D0737-04R16.
`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 The last approved version of
`www.astm.org.
`
`this historical standard is referenced on
`
`3. Terminology
`
`3.1 For definition of textile terms used in this test method:
`air permeability, and fabric, refer to Terminology D4850.
`
`3.2 For definitions of cross-machine direction; machine
`direction and other textile terms used in this test method, refer
`to Terminology D123.
`
`4. Summary of Test Method
`
`4.1 The rate of air flow passing perpendicularly through a
`known area of fabric is adjusted to obtain a prescribed air
`pressure differential between the two fabric surfaces. From this
`rate of air flow, the air permeability of the fabric is determined.
`
`5. Significance and Use
`
`5.1 This test method is considered satisfactory for accep-
`tance testing of commercial shipments since current estimates
`of between-laboratory precision are acceptable, and this test
`method is used extensively in the trade for acceptance testing.
`5.1.1 If there are differences of practical significance be-
`tween reported test results for two laboratories (or more),
`comparative tests should be performed to determine if there is
`a statistical bias between them, using competent statistical
`assistance. As a minimum, ensure the test samples to be used
`are as homogeneous as possible, are drawn from the material
`from which the disparate test results were obtained, and are
`randomly assigned in equal number to each laboratory for
`testing. The test results from the two laboratories should be
`compared using a statistical
`test for unpaired data, at a
`probability level chosen prior to the testing series. If bias is
`found, either its cause must be found and corrected, or future
`test results for that material must be adjusted in consideration
`of the known bias.
`
`5.2 Air permeability is an important factor in the perfor-
`mance of such textile materials as gas filters, fabrics for air
`bags, clothing, mosquito netting, parachutes, sails, tentage, and
`vacuum cleaners. In filtration, for example, efficiency is
`directly related to air permeability. Air permeability also can be
`used to provide an indication of the breathability of weather-
`resistant and rainproof fabrics, or of coated fabrics in general,
`and to detect changes during the manufacturing process.
`
`Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
`
`1
`
`
`
`Copyright by ASTM Int'l (all rights reserved); Wed Sep 27 15:32:26 EDT 2017
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`Bedgear 2006
`Fredman v. Bedgear
`IPR2017-00351
`
`

`

`D737 − 04 (2016)
`
`5.3 Performance specifications, both industrial and military,
`have been prepared on the basis of air permeability and are
`used in the purchase of fabrics where permeability is of
`interest.
`5.4 Construction factors and finishing techniques can have
`an appreciable effect upon air permeability by causing a change
`in the length of airflow paths through a fabric. Hot calendaring
`can be used to flatten fabric components, thus reducing air
`permeability. Fabrics with different surface textures on either
`side can have a different air permeability depending upon the
`direction of air flow.
`5.4.1 For woven fabric, yarn twist also is important. As twist
`increases, the circularity and density of the yarn increases, thus
`reducing the yarn diameter and the cover factor and increasing
`the air permeability. Yarn crimp and weave influence the shape
`and area of the interstices between yarns and may permit yarns
`to extend easily. Such yarn extension would open up the fabric,
`increase the free area, and increase the air permeability.
`5.4.2 Increasing yarn twist also may allow the more circular,
`high-density yarns to be packed closely together in a tightly
`woven structure with reduced air permeability. For example, a
`worsted gabardine fabric may have lower air permeability than
`a woolen hopsacking fabric.
`
`6. Apparatus
`6.1 Air Permeability Testing Apparatus4consisting of the
`following:
`6.1.1 Test Head that provides a circular test area of 38.3 cm2
`(5.93 in.2)6 0.3 %.
`NOTE 1—Alternate test areas may be used, such as 5 cm2 (0.75 in.2),
`6.45 cm2 (1.0 in.2), and 100 cm2 (15.5 in.2).
`6.1.2 Clamping System to Secure Test Specimens, of differ-
`ent thicknesses under a force of at least 50 6 5 N (11 6 1 lbf)
`to the test head without distortion and minimal edge leakage
`underneath the test specimen.
`6.1.2.1 A suitable means to minimize edge leakage is to use
`a 55 Type A durometer hardness polychloroprene (neoprene)
`clamping ring 20 mm (0.75 in.) wide and 3 mm (0.125 in.)
`thick around the test area above and underneath the test
`specimen.
`
`NOTE 2—Since air leakage may affect test results, precautions must be
`taken, especially with very heavy or lofty fabrics, to prevent leakage. The
`use of a weighted ring and rubber gaskets on the clamp surfaces has been
`found to be helpful. Methods F778 describes a series of usable clamping
`adaptions to eliminate edge leakage. Gaskets should be used with caution
`because in some cases, and with repeated-use gaskets may deform
`resulting in a small change in test area. A weighted ring can be used with
`fabrics, such as knits or those that readily conform to the test head. The
`weighted ring is not recommended for lofty or stiff fabric.
`6.1.3 Means for drawing a steady flow of air perpendicu-
`larly through the test area and for adjusting the airflow rate that
`preferably provides pressure differentials of between 100 and
`2500 Pa (10 and 250 mm or 0.4 and 10 in. of water) between
`the two surfaces of the fabric being tested. At a minimum, the
`
`4 For additional information on obtaining apparatus, equipment, or supplies that
`may be suitable for use in this standard, please visit the ASTM Manufacturers’
`Equipment Directory at www.astm.org.
`
`test apparatus must provide a pressure drop of 125 Pa (12.7
`mm or 0.5 in. of water) across the specimen.
`6.1.4 Pressure Gage or Manometer, connected to the test
`head underneath the test specimen to measure the pressure drop
`across the test specimen in pascals (millimetres or inches of
`water) with an accuracy of 62 %.
`6.1.5 Flowmeter, volumetric counter or measuring aperture
`to measure air velocity through the test area in cm3/s/cm2
`(ft3/min/ft2) with an accuracy of 62 %.
`6.1.6 Calibration Plate, or other means, with a known air
`permeability at the prescribed test pressure differential to verify
`the apparatus.
`6.1.7 Means of calculating and displaying the required
`results, such as scales, digital display, and computer-driven
`systems.
`6.2 Cutting Dies or Templates, to cut specimens having
`dimensions at least equal to the area of the clamping surfaces
`of the test apparatus (optional).
`
`7. Sampling and Test Specimens
`7.1 Lot Sample—As a lot sample for acceptance testing,
`randomly select the number of rolls or pieces of fabric directed
`in an applicable material specification or other agreement
`between the purchaser and the supplier. Consider the rolls or
`pieces of fabric to be the primary sampling units. In the
`absence of such an agreement, take the number of fabric rolls
`or pieces specified in Table 1.
`
`NOTE 3—An adequate specification or other agreement between the
`purchaser and the supplier requires taking into account the variability
`between rolls or pieces of fabric and between specimens from a swatch
`from a roll or piece of fabric to provide a sampling plan with a meaningful
`producer’s risk, consumer’s risk, acceptable quality level, and limiting
`quality level.
`take a
`7.2 Laboratory Sample—For acceptance testing,
`swatch extending the width of the fabric and approximately 1
`m (1 yd) along the lengthwise direction from each roll or piece
`in the lot sample. For rolls of fabric, take a sample that will
`exclude fabric from the outer wrap of the roll or the inner wrap
`around the core of the roll of fabric.
`7.3 Test Specimens—From each laboratory sampling unit,
`take ten specimens unless otherwise agreed upon between
`purchaser and supplier. Use the cutting die or template de-
`scribed in 6.2, or if practical, make air permeability tests of a
`textile fabric without cutting.
`7.3.1 Cutting Test Specimens—When cutting specimens, cut
`having dimensions at least equal to the area of the clamping
`mechanism. Label to maintain specimen identity.
`7.3.1.1 Take specimens or position test areas representing a
`broad distribution across the length and width, preferably along
`the diagonal of the laboratory sample, and no nearer the edge
`
`TABLE 1 Number of Rolls or Pieces of Fabric in the Lot Sample
`Number of Rolls or Pieces in
`Number of Rolls or Pieces
`Lot, Inclusive
`in Lot Sample
`1 to 3
`4 to 24
`25 to 50
`over 50
`
`all
`4
`5
`10 % to a maximum of 10 rolls or pieces
`
`2
`
`
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`

`D737 − 04 (2016)
`
`than one tenth its width unless otherwise agreed upon between
`the purchaser and supplier. Ensure specimens are free of folds,
`creases, or wrinkles. Avoid getting oil, water, grease, and so
`forth, on the specimens when handling.
`
`8. Preparation of Test Apparatus and Calibration
`8.1 Set-up procedures for machines from different manufac-
`turers may vary. Prepare and verify calibration of the air
`permeability tester as directed in the manufacturer’s instruc-
`tions.
`8.2 When using microprocessor automatic data gathering
`systems, set the appropriate parameters as specified in the
`manufacturer’s instructions.
`8.3 For best results, level the test instrument.
`8.4 Verify calibration for the range and required water
`pressure differential that is expected for the material to be
`tested.
`
`9. Conditioning
`9.1 Precondition the specimens by bringing them to ap-
`proximate moisture equilibrium in the standard atmosphere for
`preconditioning textiles as specified in Practice D1776.
`9.2 After preconditioning, bring the test specimens to mois-
`ture equilibrium for testing in the standard atmosphere for
`testing textiles as specified in Practice D1776 or, if applicable,
`in the specified atmosphere in which the testing is to be
`performed.
`9.3 When it is known that the material to be tested is not
`affected by heat or moisture, preconditioning and conditioning
`is not required when agreed upon in a material specification or
`contract order.
`
`10. Procedure
`10.1 Test the conditioned specimens in the standard atmo-
`sphere for testing textiles, which is 21 6 1°C (70 6 2°F) and
`65 6 2 % relative humidity, unless otherwise specified in a
`material specification or contract order.
`10.2 Handle the test specimens carefully to avoid altering
`the natural state of the material.
`10.3 Place each test specimen onto the test head of the test
`instrument, and perform the test as specified in the manufac-
`turer’s operating instructions.
`10.3.1 Place coated test specimens with the coated side
`down (towards low pressure side) to minimize edge leakage.
`10.4 Make tests at the water pressure differential specified
`in a material specification or contract order. In the absence of
`a material specification or contract order, use a water pressure
`differential of 125 Pa (12.7 mm or 0.5 in. of water).
`10.5 Read and record the individual test results in SI units as
`cm3/s/cm2 and in inch-pound units as ft3/min/ft2 rounded to
`three significant digits.
`10.5.1 For special applications, the total edge leakage un-
`derneath and through the test specimen may be measured in a
`separate test, with the test specimen covered by an airtight
`cover, and subtracted from the original test result to obtain the
`effective air permeability.
`
`10.6 Remove the tested specimen and continue as directed
`in 10.3 – 10.5 until ten specimens have been tested for each
`laboratory sampling unit.
`10.6.1 When a 95 % confidence level for results has been
`agreed upon in a material specification or contract order, fewer
`test specimens may be sufficient. In any event, the number of
`tests should be at least four.
`
`11. Calculation
`11.1 Air Permeability, Individual Specimens—Calculate the
`air permeability of individual specimens using values read
`directly from the test instrument in SI units as cm3/s/cm2 and in
`inch-pound units as ft3/min/ft2, rounded to three significant
`digits. When calculating air permeability results, follow the
`manufacturer’s instructions as applicable.
`
`NOTE 4—For air permeability results obtained 600 m (2000 ft) above
`sea level, correction factors may be required.
`11.2 Air Permeability, Average—Calculate the average air
`permeability for each laboratory sampling unit and for the lot.
`11.3 Standard Deviation, Coeffıcient of Variation—
`Calculate when requested.
`11.4 Computer-Processed Data—When data are automati-
`cally computer-processed, calculations are generally contained
`in the associated software. It is recommended that computer-
`processed data be verified against known property values and
`its software described in the report.
`
`12. Report
`12.1 Report that the air permeability was determined in
`accordance with Test Method D737. Describe the material or
`product sampled and the method of sampling used.
`12.2 Report the following information for each laboratory
`sampling unit and for the lot as applicable to a material
`specification or contract order:
`12.2.1 Air permeability.
`12.2.2 When calculated, the standard deviation or the coef-
`ficient of variation.
`12.2.3 Pressure differential between the fabric surfaces.
`12.2.4 For computer-processed data, identify the program
`(software) used.
`12.2.5 Manufacturer and model of test instrument.
`12.2.6 Any modification of this test method or equipment
`including changing or adding gaskets.
`
`13. Precision and Bias5
`13.1 Summary—In comparing two averages, the differences
`should not exceed the single-operator precision values shown
`in Table 2 for the respective number of tests, and for fabrics
`having averages similar to those shown in Table 3, in 95 out of
`100 cases when all the observations are taken by the same
`well-trained operator using the same piece of equipment and
`specimens randomly drawn from the sample of fabrics. Larger
`differences are likely to occur under all other circumstances.
`
`5 Supporting data have been filed at ASTM International Headquarters and may
`be obtained by requesting RR:D13-1109.
`
`3
`
`
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`D737 − 04 (2016)
`
`TABLE 2 Air Permeability, ft3/min/ft2, Critical DifferencesA for the
`Conditions Noted
`Number of
`Observations
`in Each
`Average
`
`Within-
`Laboratory
`Precision
`
`Between-
`Laboratory
`Precision
`
`Materials
`
`Single-
`Operator
`Precision
`
`Woven Fabrics
`Plain, Oxford spun
`yarns, Material 5
`
`Plain, spun yarns,
`Material 6
`
`Plain, continous
`filament yarns,
`Material 7
`
`Nonwoven Fabrics
`Hydroentangled
`
`Dry-laid
`
`Meltblown
`
`Needlepunch
`
`Resin-bonded
`
`Spun-bonded
`
`Thermal
`
`Wet-laid
`
`1
`
`2
`5
`10
`1
`
`2
`5
`10
`1
`
`2
`5
`10
`
`1
`2
`5
`10
`1
`2
`5
`10
`1
`2
`5
`10
`1
`2
`5
`10
`1
`2
`5
`10
`1
`2
`5
`10
`1
`2
`5
`10
`1
`2
`5
`10
`
`28.8
`
`20.3
`12.9
`9.1
`9.7
`
`6.9
`4.3
`3.1
`2.8
`
`2.0
`1.3
`0.9
`
`27.6
`19.5
`12.3
`8.7
`51.3
`36.3
`23.0
`16.2
`8.8
`6.2
`4.0
`2.8
`100.7
`71.2
`45.0
`31.8
`162.7
`115.1
`72.8
`51.5
`234.6
`165.9
`104.9
`74.2
`206.2
`145.8
`92.2
`65.2
`1.34
`0.95
`0.60
`0.43
`
`34.1
`
`27.4
`22.4
`20.5
`13.0
`
`11.0
`9.6
`9.1
`2.8
`
`2.0
`1.3
`0.9
`
`33.9
`27.7
`23.3
`21.6
`55.6
`42.1
`31.3
`26.8
`9.3
`6.9
`4.9
`4.0
`112.4
`87.0
`67.3
`59.2
`179.8
`138.1
`105.4
`92.0
`234.6
`165.9
`104.9
`74.2
`232.3
`180.8
`141.2
`125.2
`2.80
`2.63
`2.52
`2.49
`
`59.3
`
`55.7
`53.4
`52.6
`30.4
`
`29.6
`29.1
`29.0
`4.4
`
`3.8
`3.5
`3.4
`
`52.0
`48.2
`45.8
`45.0
`73.4
`63.8
`57.2
`54.9
`21.5
`20.6
`20.0
`19.8
`113.4
`88.2
`68.8
`61.0
`189.2
`150.1
`120.8
`109.3
`251.2
`188.7
`138.1
`116.5
`232.2
`180.8
`141.2
`125.2
`3.24
`3.10
`3.01
`2.98
`
`A The critical differences were calculated using t = 1.960, which is based on infinite
`degrees of freedom.
`
`13.2 Woven Fabrics, Interlaboratory Test Data—An inter-
`laboratory test was run in 1994 through 1995 in which
`randomly drawn samples of three fabrics were tested in each of
`eight laboratories. Two operators in each laboratory each tested
`eight specimens of each fabric using this test method. Four of
`the eight specimens were tested on one day, and four speci-
`mens were tested on a second day. Analysis of the data was
`conducted using Practices D2904 and D2906. The components
`of variance for air permeability expressed as standard devia-
`tions were calculated to be the values listed in Table 3. The
`three woven fabric types were:
`
`4
`
`TABLE 3 Air Permeability, ft3/min/ft2
`Components of Variance Expressed as
`Standard DeviationsA
`Between-
`Within-
`Single-
`Laboratory
`Laboratory
`Operator
`Component
`Component
`Component
`
`Grand
`Average
`
`Materials
`
`Woven Fabrics
`Plain, Oxford
`spun yarns Mat 5
`Plain, spun yarns
`Mat 6
`Plain, continous
`filament yarns
`Mat 7
`Nonwoven Fabrics
`Hydroentangled
`Dry-laid
`Meltblown
`Needlepunch
`Resin-bonded
`Spun-bonded
`Thermal
`Wet-laid
`
`217.0
`
`90.0
`
`8.3
`
`220.0
`402.0
`72.7
`278.0
`948.0
`474.0
`564.0
`17.2
`
`10.4
`
`3.5
`
`1.0
`
`9.9
`18.5
`3.2
`36.0
`58.7
`84.6
`74.4
`0.5
`
`6.6
`
`3.1
`
`0.0
`
`7.1
`7.7
`1.0
`18.0
`27.5
`0.0
`38.6
`0.9
`
`17.5
`
`9.9
`
`1.2
`
`14.2
`17.3
`7.0
`5.3
`21.3
`32.4
`0.0
`0.6
`
`A The square roots of the components of variance are being reported to express
`the variability in the appropriate units of measure rather than as the squares of
`those units of measure.
`
`Material 5—S/2438, Plain Weave, Oxford, Spun Yarns
`Material 6—S/0002H, Plain Weave, Spun Yarns
`Material 7—S/28305, Plain Weave, Continuous Filament Yarns
`13.3 Nonwoven Fabrics, Interlaboratory Test Data—An
`interlaboratory test was run in 1994 in which randomly drawn
`samples of eight fabrics were tested in each participating
`laboratory. Two operators in each laboratory each tested eight
`specimens of each fabric using this test method. Four of the
`eight specimens were tested on one day and four specimens
`were tested on a second day. Analysis of the data was
`conducted using Practices D2904 and D2906. The components
`of variance for air permeability of nonwoven fabrics expressed
`as standard deviations were calculated to be the values listed in
`Table 3. The eight fabric types and number of participating
`laboratories were as follows:
`Number of Participating Laboratories
`Nonwoven Material
`5
`Hydroentangled
`5
`Dry-Laid
`5
`Meltblown
`5
`Needlepunched
`2
`Resin-Bonded
`4
`Spun-Bonded
`4
`Thermal
`5
`Wet-Laid
`13.4 Precision—For the components of variance reported in
`Table 3, two averages of observed values should be considered
`significantly different at
`the 95 % probability level
`if the
`difference equals or exceeds the critical differences listed in
`Table 2. There were sufficient differences related to the fabric
`type and structure to warrant
`listing the components of
`variance and the critical differences separately. Consequently,
`no multi-fabric comparisons were made.
`
`NOTE 5—The tabulated values of the critical differences should be
`considered to be a general statement, particularly with respect to between-
`laboratory precision. Before a meaningful statement can be made about
`two specific laboratories, the amount of statistical bias, if any, beteween
`them must be established with each comparison being based on recent data
`obtained on specimens taken from a lot of fabric to the type being
`
`
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`D737 − 04 (2016)
`
`evaluated so as to be as nearly homogeneous as possible, and then
`randomly assigned in equal numbers to each of the laboratories.
`NOTE 6—Since the interlaboratory test for resin-bonded nonwoven
`fabric included only two laboratories and the spun-bonded and thermal
`nonwoven fabrics included only four laboratories, estimates of between
`laboratory precision may be either underestimated or overestimated to a
`considerable extent and should be used with special caution.
`
`13.5 Bias—The value of air permeability only can be
`defined in terms of a test method. Within this limitation, this
`test method has no known bias.
`
`14. Keywords
`14.1 air permeability; fabric
`
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