The water intrusion pressure (WIP) is an indirect gauge of the pore size and hydrophobicity of a filter membrane. It is the pressure required for pushing water through a hydrophobic filter membrane.
The pressure in bar is measured, with the application of which a water droplet appears for the first time on a side of the membrane after it has been pushed through the other side. The smaller the pore size and the greater the hydrophobicity of a filter membrane are, the higher is the pressure required to push water through the membrane.
A typical WIP e.g. of TRAKETCH® PET with a pore size of 0.2 µm is ≥3.5 bar and of TRAKETCH® PET with a pore size of 0.4 µm is ≥1.8 bar. With a pore size of 1.2 µm, the WIP of TRAKETCH® PET is still close to ≥0.6 bar.