What is Air Permeability Test of Textile?

The air permeability test is a test method for measuring the air permeability of textiles. Air permeability refers to the permeability of gases to polymer materials such as films, coatings, and fabrics. It is a fundamental property of leather products such as leather jackets, shoes, and some fabrics for use.

Fabric air permeability definition: the air permeability of fabric is a reflecting the ease of gas “particles” through the fabric. The air permeability of the fabric is often expressed in terms of ventilation property, which refers to the amount of air per unit area through the fabric in a unit of time under the specified pressure difference.

So what is the air permeability test of a fabric? In this post, I will explain three aspects: testing standards of fabric air permeability, how to test the air permeability of fabric? How to calculate and express the results of the air permeability test?

Testing standards of fabric air permeability

Currently, the following standards are commonly used for testing the air permeability of fabrics

• ASTM D737  Standard Test Method for Air Permeability of Textile Fabrics
• ISO 9237  Air Permeability Test Method of Textile Fabrics
• GB/T 5453  Determination of the permeability of fabrics to air

ISO 9237 test scope

This international Standard describes a method for measuring the permeability of fabrics to air and is applicable to most types of fabrics, including industrial fabrics for technical purpose, nonwovens and made-up textile articles that are permeable to air.

ASTM D737 test scope

This test method covers the measurement of the air permeability of textile fabrics. 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.

ASTM D737 test scope

This standard specifies a method for testing the air permeability of fabrics and is applicable to a wide range of textile fabrics, including technical fabrics, non-woven fabrics and other breathable textile articles.

How to test the air permeability of fabric?

Test principle

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 fabrics is determined.

Test procedure

Firstly, prepare the conditioning specimen and a fabric air permeability tester to ensure that they meet the requirements of the breathability test. Then clamp the specimen to the test bench, avoiding the edges and folds of the fabric in the test area. Start the air permeability tester, pass the air through the specimen, adjust the differential pressure to a stable level and record the test results.

Note: The test should be repeated several times on different parts of the same specimen under the same conditions.

How to calculate and express the results of the air permeability test?

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.

Air Permeability, Average – calculate the average air permeability for each laboratory sampling unit and for the lot.

Standard Deviation, Coefficient of Variation-Calculate when requested.

Computer-processed Data: When data are automatically 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.

The specific calculation formula is as follows.

Calculate the arithemetic mean of the individual readings and the coefficient of variation (to the nearest 0.1%), stating the 95% confidence interval.

Calculate the air permeability, R, expressed in millimetres per second, using the equation

R = Qv / A * 167

Where

• Qv: the arithmetic mean flowrate of air, in cubic decimetres per minute (litres per minute).
• A: the area of fabric under test, in square centimetres.
• 167: the conversion factor from cubic decimetres (or litres) per minute persquare centimetre to millimetres per second.

For open fabrics and nonwovens, the air permeability R may be expressec in metres per second using the equation R = Qv / A * 0.167

Express the 95% confidence interval in the units specified in the formula, rounding the result R obtained above to 2% of the value.