What is the design principle of a waterproof and breathable valve?

A waterproof and breathable valve uses expanded PTFE from Puyi as its breathable membrane; at the microscopic level, this membrane has a porous structure. By taking advantage of the difference in size and order of magnitude between gas molecules and liquid droplets as well as dust particles, gas molecules can pass through while liquids and dust cannot, thereby achieving the purpose of being waterproof and breathable. Water is generated because, during operation, the product draws in water vapor under negative pressure; when this vapor condenses inside the inner shell, water appears. After installing the Puwei waterproof and breathable valve, air is filtered through the PUW waterproof and breathable membrane under negative pressure; the air drawn in contains trace amounts of water vapor. Even under positive pressure, this vapor can be expelled, thereby achieving a balanced pressure difference between the inside and outside – allowing for breathability while also preventing water from forming. I don’t understand; I searched for it. .