This work reports the effect of temperature and pressure on the permeability, diffusion and solubility coefficients of N-2, O-2, and CO2 in natural rubber reinforced with different amounts of cellulose. The values of the permeability coefficient of carbon dioxide, oxygen and nitrogen in these materials are significantly smaller than in natural rubber. The curves representing the dependence of the permeability coefficient on the pressure of the upstream-chamber, exhibit an upturn in the low pressure region as the pressure decreases. The isotherms showing the dependence of the diffusion coefficient on the pressure of the upstream chamber exhibit the same pattern as those of the permeability coefficient. The experimental results are interpreted in terms of changes in the free volume in the polymer membranes.