Waterproof breathable

Waterproof breathable fabrics are one of the great innovations in outdoor gear. GoreTex is the originator, though there are many imitators now that Gore's older patents have expired.

The fabrics are made by laminating an expanded polytetrafluoroethylene (ePTFE - essentially, expanded Teflon) layer inside a nylon, polyester or other fabric. The ePTFE is a porous, hydrophobic material. The pore size is small enough to prevent water in liquid form from passing through but large enough for gaseous water to pass. This is the secret of its waterproof breathability - liquid water is kept out but water vapour is released.

Key to the effective waterproofness and breathability of the fabric is the durable water repellancy (DWR) of the outer layer. If the outer layer of fabric soaks up water, it compromises the properties of the GoreTex . For that reason, it is important to keep the outer layer clean and the DWR in good shape. Frequent washing and machine drying is essential - the heat will keep the DWR coating intact.

Another key to maintaining the quality of the laminate is a good lining. Without the lining, the laminate is easier to damage. Two-layer fabrics need a separate liner, usually a light, breathable lining fabric or mesh. Three-layer fabrics dispense with a separate liner an use a bonded layer - usually a tricot that gives the inside of the fabric a greyish colour. Some very light versions use a pattern of very small dimples on the laminate.

Do these fabrics really work? That depends on your expectations.

First of all, no garment is going to keep you from sweating. If you are generating more heat than you can get rid of, you will sweat. Even at very low activity levels, your body is releasing insensible (not noticable) perspiration. If you are generating liquid sweat, you need to cool off or get a towel. If you are only generating insensible perspiration (water vapour), then the fabric will allow it to pass through and you will be comfortable without condensation inside the jacket. Those who have realistic expectations find that waterproof breathable fabrics work well and are more comfortable than non-breathable fabrics.