O-Ring Permeation Chart

Learn About O-Ring Permeation Rate and Permeation Coefficients

Permeability or permeation of gases through an O-ring varies by material type; material hardness; degree of squeeze; presence or absence of lubrication; size of O-ring cross section; and the pressure, temperature and type of gas being sealed.

Typically, harder compounds containing more carbon black feature lower diffusion rates. Increased seal squeeze results in decreased permeability. Externally lubricated O-rings can decrease permeability.

FKM Viton® O-Rings are commonly used in vacuum applications due to lower permeation which impacts vacuum pump-down time and the ultimate vacuum level achievable. O-Ring permeation can also affect the accuracy of sensitive sensor and test equipment. O-Ring outgassing or leaching of internal substances can also impact sensor effectiveness. Marco Rubber offers FKM Viton® O-Rings with an additional post cure or vacuum baking resulting in lower outgassing O-Rings.

O-ring Permeation
Q = K A (P1 - P2) / D
Q is the permeation rate (cm3/sec)
K is the permeation coefficient (cm3 cm/sec cm2 atm)
A is the area (cm2)
P1 - P2 is the pressure gradient (atm)
D is the thickness (cm)

Permeation Coefficients (10-8 sccm - cm/sec - cm2 - atm)

Buna-N 8 2.5 760 0.1 25
EPDM 25-30 16-18 6-7 85
Silicone 250 75-450 8000 200 2000
Fluorosilicone 140 80 40 400
FKM Viton ® A 9-22 1-2 40 0.05-0.7 5
FKM Viton ® GF 30 3 2
Markez ® FFKM 60-80 6-8 90-100 8-12
KEL-F 0.1 0.1 0.5
PTFE 0.4 0.14 0.12
Polyimide 1.9 0.1 0.3 0.2

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