The breakthrough time of butyl, nitrile, and natural-rubber sheets (cured) of different compositions against a potent chemical warfare (CW) agent have been determined using the spot disc test (SDT) method. It was observed that butyl rubber is the best material in comparison to nitrile and natural rubber for protection against sulfur mustard (SM). One of the butyl formulations provides more than 100 h protection against SM. The diffusion coefficient of oxygen mustard (SM analog) for the same formulation (F-8) and one nonblack butyl formulation (F-5) was determined by weight gain as well as by FTIR-ATR methods. Both methods provide consistent results and the diffusion coefficient of oxygen mustard (OM) for butyl rubber is in the order of 10(-9) cm(2)/s. The diffusion coefficient of SM for the formulation Fg and F, was also determined from the SDT retardation time.