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 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 thicknessĀ¹ 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 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 D1434-63T
** ASTM E96-63T

Download the table here.