o-rings and seals

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Home > Tips > FEP Encapsulated O-ring Part 1


Tip: FEP Encapsulated O-ring Part 1

(This tip is about the characteristics the encapsulating FEP brings to the o-ring)

Because FEP is a hard plastic rather than a stretchy elastomer, it is uncommon to see an o-ring that is made entirely of TFE or FEP. However, there are applications where FEP is the perfect material. For example some automotive steering systems use FEP o-rings for fittings and they are also used in paint guns. (By the way, a tip on installing these rigid seals is to heat them in hot water before the installation so they will be slightly bigger and slip on easier.)

When someone says they want a FEP o-ring they may actually be talking about a FEP encapsulated o-ring. Here the FEP is made into a jacket or sleeve that will completely enclose an elastomer which has the desired mechanical properties needed for the o-ring, such as resistance to cold flow. Since FEP is practically chemically inert it allows the o-ring to resist almost all chemicals and will not allow corrosive fluids or gases to harm the elastomer.

The extremely low coefficient of friction of FEP makes the encapsulated o-ring an ideal choice where surface wear might otherwise be a problem. By itself, the material FEP exhibits a useful service life from below -100° F, to temperatures of over 500° F. Its resistance to solvents remains excellent throughout a wide range of temperatures. In addition, the low dielectric constant and electrical resistance also remain intact throughout this range.

Some of the advantages of this material are:

  • Corrosion resistant
  • Abrasion resistant
  • Low absorption
  • Non-permeable
  • Uniform dimensions
  • Nonflammable
  • Reusable
  • Chemically inert
  • High impact strength
  • Smooth surface
  • No swelling
  • Comes in all sizes including metric

A FEP encapsulated o-ring is often used as a static o-ring but can be used as a rotay lip seal if abrasion is handled in some way, such as mixing the FEP with graphites.

FEP encapsulated o-rings are manufactured in AS568 standard sizes. However, since they are not molded in the same way as o-rings mamufactured from one material, the inside diameter is not necessarily the same as a molded seal. The encapsulated o-ring will have a greater cross-sectional and inside diameter tolerance range than that of the AS568 standards.

The chart below gives general information on a FEP o-ring. The properties of an encapsulated o-ring will be somewhat different than that of this plastic by itself.



test method


Tensile strength
at yield
D-638 3000
at yield
at fail

NR *
Flexual Modulus
at yield
10,000 psi
D-790 500
Isod impact
strength notched
D-256 3.0
Delflection temp.
at 66 psi

at 264 psi

degrees F (degrees C)

degrees F (degrees C)
260 (127)

132 (55)
Melting point degrees F
degrees C
D-789 612
V/mil D-149 600
ohm-cm D-257 >1 x 10E+18
Water absorption %/24hr. D-570 <.01
UL flammability ----- UL 94 94 V-0
----- R, M
Flexural Strength 10,000 psi
D-638 No break
ft squared-degrees F
W/m-degrees C
Specific Gravity ----- D-792 2.2
Max. service
degrees F
degrees C
----- 500

* NR = Not Reported.

Please Note: To the best of our knowledge, the information contained in this guide is accurate, is based upon accepted technical practices and is believed to be reliable. Final determination of suitability of any process or material is the sole responsibility of the user. PSP, Inc. does not assume any liability for the accuracy or completeness of this information.

Please call us if you need help in choosing a TFE o-ring or a FEP encapsulated o-ring for your application.


FEP encapsulated o-ring Part 2



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