Any practical technique to determine the diffusivity of chemical warfare agents in protective barrier materials should require handling only miniscule volume of the chemicals and also require data analysis methods that are not computationally burdensome. Such an approach is described here based on imaging the time evolution of1L sessile drop profiles on the barrier surface and using an approximate analytical approach to analyze the time-dependent drop volume and contact angle data for extracting the diffusivity. The approximate analytical approach is validated by comparison against results from computationally intensive finite element simulations available in the literature. The domain of reliable use of the sessile drop technique in terms of the relative importance of the simultaneous evaporation and absorption is assessed using measurements on three challenging toxic chemicals in air and in butyl rubber. The ability of this approach to provide reasonable diffusivity estimates even if the substrate undergoes swelling is explored by studying water sessile drops on a Nafion membrane. The results allow one to conclude that the sessile drop technique coupled to the approximate analytical approach can be reliably used for rapid screening of new barrier materials for protection against chemical warfare agents if the screening is implemented using simulants with low vapor pressures. GRAPHICS.