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Barrier Properties Due to the  physical properties of Parylene and the method of deposition, Parylene forms a  pin-hole free film on the subject substrate. Therefore, it provides an excellent  barrier to both liquids and gases. The table below lists the permeability  characteristics of the Parylenes and also shows typical values for other types  of conformal coatings. Moisture vapor permeability values have been  measured at thickness¹ below 0.1 micron. Normalized to equivalent thickness, the  values are the same for all thicknesses. Assuming that parylene C at 0.001 inch  is pinhole free, then parylene C films at 0.1 micron (~ x 10-6 inch)  are also pinhole free. Barrier Properties of Parylene C Compared with  Epoxies, Silicones, and Urethanes POLYMER GAS PERMEABILITY cc-mil/100 in2 -  24 hours * MOISTURE VAPOR TRANSMISSION gm-mil/100  in2 - 24 hours ** N2 O2 CO2 H2 Parylene C 0.6 5 14 110 1 Epoxies 4 5-10 8 110 1.79-2.38 Silicones ... 50,000 300,000 45,000 4.4-7.9 Urethanes 80 200 3,000 ... 2.4-8.7 *  ASTM D1434-63T ** ASTM E96-63T