Comments on expressing the permeability of polymers to gases

The fundamentals of permeability and diffusivity are presented briefly to demonstrate the possible dimensional forms available in principle for expressing the coefficients of permeability (P m ) and diffusion (D m ). The interrelation between P m and D m is discussed and two recent experimental methods specific to the permeation of oxygen are summarised. Twenty‐nine units appearing for P m in the litearture are discussed and corrected where necessary. On the basis of its convenience, one particular unit is recommended and conversion factors to it are tabulated.