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 gasses. 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 **
POLYMER	N₂	O₂	CO₂	H₂
Parylene C	0.6	5	14	110	1
Epoxies	4	5-10	8	100	1.79-2.38
Silicon	...	50,000	300,000	45,000	4.4-7.9
Urethanes	80	200	3,000	...	2.4-8.7

* ASTM D1434-82 (2015) E1
** ASTM E96/E96M-16

Download the Barrier Properties table here.

Barrier Properties

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