Outdoor garments are expected to assume the functions of human skin.
At first glance, the two key requirements for a "breathable" coating seem impossible to reconcile because their demands are inherently opposite. To overcome this apparent incompatibility, several "Maxwell's Demons"1 were invented capable of distinguishing between the two forms of water: liquid and vapor. These "smart" polymeric compositions were branded "breathable." Strictly speaking, products permeable to water vapor should be called "perspirable," but the breathable designation is generally accepted by the textile industry.