The physical parameters of the xylene isomers (the positional isomers o-, m-, and p-xylenes and the skeletal isomer ethyl benzene) responsible for the differing permeation behavior of the isomers through lined unsupported 0.41 mm thick nitrile glove material were investigated. An ASTM type permeation cell at 30 degrees C, constant mixing conditions, hexane liquid collection, and capillary column gas chromatography/ mass spectrometry of samples taken from the collection side every ten minutes allowed break through times t(b) and steady-state sections to be defined. While pure isomers had distinct break through times t(b) (m-xylene = p-xylene < ethyl benzene = o-xylene), steady-state permeation rates P-s (p-xylene > m-xylene > ethyl benzene = o-xylene), lag times t(l) (m-xylene < p-xylene = ethylbenzene < o-xylene), and diffusion coefficients D-p (m-xylene < p-xylene = ethyl benzene < o-xylene), such behavior was lost in a equal volume mixture (t(b), t(l), P-s, and D-p were equivalent). The average P-s of the mixture isomers of equal volumes did not differ from that expected from the individual pure isomer P-s values. The results for the pure isomers were attributed to o-xylene and ethyl benzene being similarly sterically hindered, the p-xylene being the flattest and most symmetrical molecule and having no dipole moment, and m-xylene being intermediate in steric structure. The pure isomer t(l) were directly related to viscosity divided by the log octanol-water coefficient, while their log P-s was inversely related to dipole moment times the logarithm of the capacity factor for water for a reversed-phase high-performance liquid chromatography column. In an equivolume mixture of the isomers, isomer interactions caused equivalence for all permeation kinetic parameters, indicating that the kinetics of mixture constituents is not predictable from the behavior of the pure constituents, although mass transfer appears additive.