The rate of diffusion of gases through the paper on cigarettes and the wrapper of little cigars influences the smolder rate as well as the delivery of mainstream gaseous components. The authors employed a cell to measure the diffusion resistance of a variety of types of paper and sheets of reconstituted tobacco. The variables studied included basic weight, thickness, mineral filler species and amount, and air permeability. Variables in the papermaking technique were also investigated, as were fibers of different biological origin. The results were expressed in terms of equivalent thickness and open area. The diffusion resistance of the wrapper materials was correlated with the performance of these wrappers on cigarettes and cigars.