Can waterproof breathable membranes repel vapor?

The reason why waterproof and breathable membranes cannot block water vapor very well is that in the state of water vapor, water vapor particles are very small. According to the principle of diffusion movement or capillary movement, water vapor molecules can enter and exit through the micropores of the waterproof breathable membrane material. Vapor permeability occurs when it spreads from the inside out. When water vapor condenses into water droplets, due to the surface tension of the water droplets (molecular interaction force), the water droplet particles become larger, and the particle size of the water droplets is much larger than the pore diameter of the waterproof and breathable membrane, and the water molecules It cannot break away from the water droplets and penetrate back to the other side (inside). This is the reason why the waterproof breathable membrane material can block water vapor, but this is the principle of waterproofing of the breathable membrane raw material, which makes the waterproof breathable membrane waterproof. This powerful feature.
In terms of the current development technology level of waterproof and breathable membrane materials (ePTFE expanded polytetrafluoroethylene), the diameter of the very small passing objects that the waterproof and breathable membrane materials can prevent is 0.02 microns (μm), and water vapor is composed of water vapor molecules. The diameter of water vapor molecules is about 0.0004 microns (μm), so the waterproof and breathable membrane cannot prevent the entry and exit of water vapor.
Water vapor generally exists in a gas-liquid two-phase form, in which the liquid phase can exist in the form of a "mist" dispersed form (water vapor is the gaseous form of water), or it can exist in the form of accumulation of a large number of droplets. In the actual application of products from waterproof and breathable membrane processing manufacturers, most of what they come into contact with refers to "water vapor", such as environments with high humidity, rainy weather, etc.