O-ring lexicon

Shore hardness

Shore hardness indicates how soft or hard an O-ring material is. It is measured using a standardized testing device on a scale from 0 to 100; for O-rings, this is usually Shore A.

What is Shore hardness?

Shore hardness describes an elastomer’s resistance to penetration by a standardized test indenter. The deeper the indenter penetrates, the softer the material and the lower the Shore value. The Shore A scale is used for soft to medium-hard materials, such as most O-ring elastomers, while the Shore D scale is used for hard materials, such as PTFE. A typical O-ring has a Shore A value of approximately 70 to 90.

Why Shore hardness is important for O-rings

Hardness determines how the seal behaves in the installation space. Softer O-rings (around 70 Shore A) conform better to surfaces and seal even with minimal compression, but are more susceptible to gap extrusion at high pressure. Harder O-rings (around 90 Shore A) better withstand high pressure and tight gaps, but require greater compression to do so. The correct hardness is therefore always a balance between pressure, gap size, and surface.

Hardness in the NH range

The values are reported as rounded nominal values with a tolerance of ±5 Shore:

FKM: 70 to 75 Shore A
FFKM (ECOLAST®): 70 to 90 Shore A, depending on the compound
FEP-coated: 90 Shore A
PTFE: 60 Shore D

Key Points at a Glance

Shore hardness measures how hard an O-ring is, usually in Shore A; for PTFE, it is measured in Shore D.
Soft material seals more easily, while hard material better resists pressure and gap extrusion.
The exact hardness for each mixture is listed in the corresponding data sheet.

You can find the hardness of each compound in the respective data sheets. You can find the right material for your application in our product range.

Go to the data sheets →