The membrane laminated to the external fabric is composed of a hydrophilic aliphatic polyether-urethane with 30% of metallic aluminum ( this gives a high heat-reflecting capacity) based on the mass of the polymer. The membrane is waterproof and breathable: the polymer is hydrophilic and transports moisture produced by the body perspiration by a chemical process called "Molecular diffusion".
Hydrophilic groups on the polymer chain transport water molecules ( by hydrogen bond) from the side with higher relative humidity (body side) to the side with lower humidity (outside), the efficiency of this process is dependant also on the difference of temperature between the two sides of the membrane.