Permeability coefficients, , for H2 in 10 different types of silicone polymer membranes were measured in the temperature range of 10.0–55.0°C and at pressures up to 100 psig (∼6.8 atm). The values of decrease slightly with increasing Δp, the pressure difference across the membranes. The permeability of silicone polymers to H2 increases with an increase in temperature; the values of the energy of activation for permeation are in the range of 1.4–4.3 kcal/mol. The substitution of different functional groups in the backbone and side chains of silicone polymers has similar effects on the permeability of the polymers to H2 as observed in earlier studies with other light gases. for H2 decreases with an increase in the bulkiness of the substituted functional groups. The substitution of Si[BOND]O bonds with stiffer Si[BOND]C bonds in the backbone chains also results in a considerable decrease in permeability.