Garment materials that provide protection against exposure to toxic chemical warfare agents (CWAs) not only require the ability to block the passage of these toxic compounds in vapor form but also the ability to transport water vapor to allow cooling for the wearer. Only a very limited number of examples of such "breathable" CWA barrier materials are known. A new type of reactive organic/inorganic composite film material is presented that has a very high water vapor transport rate (>1800 g m(-2) day(-1) for a 220-mu m-thick film) and the ability to completely block penetration of the mustard agent simulant, 2-chloroethyl ethyl sulfide (CEES), after 22 h of continuous exposure. This new composite material is based on two components: (1) a cross-linked, diol-functionalized room-temperature ionic liquid polymer that serves as a dense, flexible hydrophilic matrix, and (2) a basic zeolite (sodium zeolite-Y (NaY)) that serves as an inexpensive, nucleophilic additive that chemically degrades the CEES as it enters the film. Preliminary FT-IR studies on this new reactive barrier material suggest that the OH groups on the ionic polymer not only facilitates water vapor transport but may also help activate mustard-type vapors for reaction with the imbedded NaY.