air permeability; breathability
Technical term used in materials science, textiles, and product descriptions to indicate how well air passes through a material.
This jacket has high breathability, so it's comfortable even in summer.
It is important to choose materials with good air permeability.
防水性 means waterproofness; often discussed together with 通気性 in outdoor gear.
Compound of 通気 (air flow, ventilation) and 性 (property, -ness).