Proof and permeable
In 1969, the US American Bob Gore succeeded for the first time in developing a semipermeable membrane. Gore... Ring a bell? Gore-Tex is now used by many people as a synonym for waterproof textiles. Even though the “GTX” jackets & co. are extremely popular, nowadays there is a huge range of membranes from various manufacturers.
The is indicated by the water column. Its value tells us how high - in mm - the water pressure in the form of a column must be per square meter of fabric until it allows moisture to pass through. Most high-end hard shells are at values of 20,000 mm and above, but 10,000 mm is already sufficient in most cases. The big challenge, however, is to achieve a very good water vapour permeability aka breathability despite waterproofness. There are two big players on the market: microporous membranes made of polytetrafluoroethylene (PTFE) and non-porous membranes made of polyurethane (PU) or polyester. In Gore-Tex, whose core is a PTFE membrane, the water vapour molecules - i.e. sweat - move through over 1.4 billion/cm2 of microscopically small pores. However, these small channels can be blocked by the body's own fats and salts or even dirt. That is why - contrary to the still persistent myth - it is imperative to wash your Gore-Tex jacket when necessary.
Poreless membranes made of PU or polyester are based on a chemical-physical molecule transport. Caution getting nerdy: Hydrophilic, i.e. water-loving, components bind the water molecules and conduct them through hydrophobic, water-repellent, structures to the outside. This process accelerates the higher the temperature and humidity gradient, i.e. warmer and more humid inside than outside. If this is the case, a so-called "partial pressure" arises. So when physical activity increases, bikers literally crank up the exhaust hood. Logically, this system only really works properly up to an outside temperature of about 20 °C. For comparison: if you open the bathroom window after a hot shower on a cool day, the water vapour is drawn out much faster than on a hot summer day. However, the wafer-thin membranes alone are too fragile to be used exclusively to make clothing. For this reason, they are bonded to substrates at high temperature and "packaged". The result is a multi-layer sandwich construction called a “laminate". Commonly used are 3-, 2.5- and 2-layer laminates. As a base, they have a preferably robust, abrasion-resistant outer fabric made of nylon (polyamide) or polyester, including the membrane and on the inside either a firmly laminated lining (3-layers), an applied protective coating (2.5-layers) or a loosely suspended fabric (2-layers). 3-layer variants are considered the highest quality solution because they are more robust and durable.