SympaTex is a type of fabric that is branded as waterproof with "breatheable" fabrics made or licenced by SympaTex Technologies GmbH. The fabric features a waterproof, windproof and breatheable membrane that is laminated to fabrics either on its inner surface or sandwiched between two fabric layers (often marketed as "3 layer laminate"). The latter system offers greater durability, by better protecting the integrity of the SympaTex layer from abrasion to both the outside and the inside of the garment.

The SympaTex membrane is made of hydrophilic polyether-ester block copolymer, which is closed (i.e. it has no pores). Like its more common polyurethane equivalent, it can also be referred to as a monolithic membrane. No water can get in from the outside, but water vapour molecules are transported through the membrane from the inside to the outside by way of an absorption and evaporation process. This moisture transfer through the membrane is what is referred to as "breatheability."

A closed membrane like SympaTex differs from microporous membranes (such as eVent or now discontinued Triplepoint Ceramic) which have microscopic pores that let air (and water vapour) pass through, yet have such low surface energy that the surface tension of any (liquid) water in contact remains too high to allow it to squeeze through the pores. Microporous membranes have traditionally been let down by the contamination of their pores which significantly degrades their breatheability and commonly also have poorer adhesion to fabrics making them more susceptible to delamination.