How waterproof vents are breathable

1. Physical: Hydrophobic (fear of water) is waterproof, but vapor permeable - the pores of a microporous coating or laminate are so small that liquid water cannot pass through. However, vapour water molecules are many times smaller than liquid molecules and can pass through these "micropores".

2. Chemicals: Hydrophilic/non-porous laminates or coatings move moisture by chemical diffusion. The water molecule is positively charged, and the hydrophilic PU is negatively charged, attracting water through the intermolecular gap of the PU. Because ionic bonds are relatively weak, water is pushed through these gaps until the water vapor has passed completely.

3. Differential pressure is the difference in heat and humidity levels from one side of a material to the other. According to the second law of thermodynamics, moisture will tend to dry out. Therefore, the warm, moist air will flow to the cold, dry air until equilibrium is reached. Due to the heat and moisture of the human body, there is almost always a high level of heat and humidity inside the clothing system. This creates a pressure differential that forces heat and moisture to spread out. The greater the difference between the heat and humidity inside and outside the clothing system, the greater the pressure differential that will push the heat and humidity out.