Measurement of Fabric Air Permeability

1. Fabric air permeability

Fabric air permeability is a nature of air passing through fabric, normally under the situation that two sides of fabric exist pressure difference, that is to say, it is speed that airflow vertically goes through fabric in a prescribed test area, pressure drop and time, whose unit is “”mm/s” or “m/s”. Air permeability tester is the common used to measure it. The principle is that in a prescribed pressure difference, amount of airflow passing through a certain area of fabric in a certain time is measured, so that air permeability is calculated.

 

2. Air permeability test

a) Apparatus and materials

Air permeability tester, scissor, a variety of fabric.

 

b) Test principle

According to prescribed method and test parameter, sample is clamped on the air inlet, then adjusting winder’s speed to make two sides of fabric achieve certain pressure drop. In accordance with nozzle aperture and two sides’ pressure difference, fabric air permeability is measured. Air permeability is that amount of airflow vertically goes through per area of fabric in per unit time, under a certain pressure difference of two sides of fabric, whose unit is “mm/s”.

 

c) Test method

1 Sample preparation

The whole piece of fabric at least 1m is cut from a cloth, as test sample. It should be chosen randomly from 3m or above edge of cloth, without wrinkle and apparent spots.

 

2 Test preparation

Adjust the balance of machine; check tightness and air tightness of each connecting link of air permeability tester.

 

3 Test procedure

• Choose nozzle suitable for fabric, test area (generally 20cm^2) and pressure drop. Set parameter, calibrate, clear. Pressure drop for garments use is 100Pa, and for industry use is 200Pa. if the mentioned pressure drop can be reached or unapplicable, you can choose 50Pa or 500Pa after negotiation, or test area can use 5 cm^2, 50 cm^2, 500 cm^2 (if you use other test area, it should be stated in report). If you want to compare the test result, same test area and pressure drop should be adopted.
• Sample setting circle is chosen to mount on test bench; nozzle is chosen to mount into air measured cup.
• Machine is power-on.
• Press “Set” to set nozzle No. when the indicator light is on at the top left corner of nozzle number-displayed screen. Press “Set” again to set test area when the indicator light is on at the top left corner of air permeability/pressure drop displayed screen. Press the button again to set pressure drop of two sides of fabric when the indicator light is on at the top left corner of pressure drop displayed screen. Then press “Set” to quit.
• Sample is placed on the testbed, with straight pressure ring pressed and pressure handle pulled press it tightly. In the moment the sample fixture is installed well, press “Start” to start the test (During the test processing, pressure difference is shown on the air permeability volume displayed screen. The pressure difference should be “600~3300” when it achieves set value as displayed on pressure drop screen. Otherwise, nozzle or test area should be adjusted until it is in this range, but in general, size of nozzle is adjusted). When the pressure difference achieves the set value, air permeability will be shown automatically on the screen of pressure drop, and then the machine will stop automatically. Data of air permeability rate are recorded.
• After finishing the test, pushing down the pressure handle and pushing the ball on the handle toward inside, the handle is lifted, loosening sample pressure head to change the sample to do another same test. Under the same conditions, different parts of the same sample should be tested repeatedly for at least 10 times, recording it and calculating its average value.