Theory 075/Textiles & Fibres
Breathability Is a Pore Ratio
The claim
Waterproof-breathable performance is set by the ratio of pore size to the mean free path of water vapour rather than by pore volume.
01The mechanism
Vapour passes by diffusion when pores are comparable to the mean free path; liquid water is excluded by surface tension at the same size.
02Predictions
- P1Breathability should track the ratio.
- P2Larger pores should leak despite higher vapour flux.
03Refutation
Breathability tracking pore volume would remove the ratio.