The present invention relates to a porous adaptive membrane structure that has movable membranes (2, 2'). The structure can be made to change its gas, liquid or particulate permeability in response to surrounding environmental conditions. The application of this invention is includes protective apparel that is comfortable to wear wherein the level of protection provided is based on conditions in the environment. Hence, the protective apparel is highly- breathable and comfortable in a non-hazardous environment but impermeable or only semipermeable in a hazardous environment.