One of the main methods to test the gas permeability is using partialpressuredifference.
用压差法测试塑料薄膜的透气性，是一个长期使用的主流测试方法。
2
Permeance (P): The ratio of the gas transmission rate to the difference in partialpressure of the gas on the two sides of the film.
译文：气体透过系数（P）：单位时间内单位压力差下稳定透过单位面积上单位厚度的试样的气体体积。
3
After inflexion, the permeation flux is directly proportional to the difference of the square root of the vapour partialpressure on both sides of the membrane.