Gore-Tex membrane is formed from layers of polytetrafluoroethylene (PTFE) and polyurethane To provide waterproofing and breathability. The PTFE contains millions of tiny pores (about 14 million per millimetre square) that are small enough to stop rain penetration but large enough to let sweat molecules through.
Gore-Tex fabrics are usually part of a laminate system, often consisting of three layers.
The outer layer is a protective layer, manufactured from a strong robust fabric which is DWR treated. For Gore-Tex Pro garments this layer is even more robust.
The mid layer is the Gore-Tex membrane making the fabric waterproof, windproof and breathable.
There is not always an inner layer in all garments, this is to provide inner protection for the Gore-Tex membrane