We used a U.S.A. military respirator test with dimethyl methylphosphonate (DMMP) to compare a commercial gas mask canister to composite bed designs. These comparisons were conducted at a constant volume of 320 cm(3), equal to the total volume of the adsorbent and HEPA elements in a commercial gas mask canister, and fifty percent improvement in performance rating was experimentally demonstrated. In a second comparison, a 3-fold increase in gas life of a commercial canister with a 1.5 cm deep bed of activated carbon was experimentally demonstrated by adding a backup layer to a fully packaged commercial canister. An equation describing irreversible physical adsorption occurring in a two-layer bed and an iterative inverse solution is presented for design of composite beds utilizing polishing sorbents. An overall adsorption rate constant model is presented to predict adsorbent bed performance. A generally applicable axial dispersion model was developed for application to adsorbents enhanced by sintered microfibrous networks.