An Overview about Gasket Material Hardness

23 October 2020

The question of how hard a gasket should be comes up quite often. For an answer we need to look at what the gasket actually does. Aside from that, it is important to be familiar on how they vary depending on the gasket material used. Below is an overview about gasket material hardness.

What is the Function of a Gasket Material

The job of every gasket is to fill an uneven gap between two surfaces, forming a barrier that stops fluid moving to where it shouldn’t be. Larger gaps and more uneven surfaces need a softer gasket. For example, a gasket between two parallel machined pipe flanges can be hard, resisting loads as the joint faces are tightened together. In contrast, the gasket sealing an electrical enclosure needs to be softer and compress more because the enclosure door will tend to bend as it’s latched.

So a general rule is that a gasket should be as soft as possible in order to fill the gap between two surfaces. At the same time it must be strong enough to resist the lateral forces acting on it. For elastomeric gasket materials two parameters define hardness: Shore hardness and compression force deflection (CFD.) Here’s what these two terms mean.

Shore Hardness – Hardness in this context is a measure of how well a material resists a permanent indentation. The hardness of rubber and elastomeric materials is measured on a durometer and reported as a “Shore A” number. Very soft materials like a rubber band will be around 20, a pencil eraser is between 30 to 40, and car tires measure 60 to 70 Shore A.

Compression Force Deflection – CFD measures firmness and is defined in ASTM standard D1056 as the force needed to reduce the material in thickness by 25%. According to this standard materials are given a grade correlating to their firmness. Grade 0 material needs less than 2 psi to reduce its thickness by 25%, so is very soft. At the other end of the spectrum a grade 5 material needs at least 17 psi to achieve the same compression. A gasket material that compresses easily accommodates variation in the gap between two surfaces without needing more closing force than can be applied by the clamps or latches.

Know more about gasket material hardness from VSRP. We are an Australian based company with a subsidiary manufacturing facility in Vietnam and close and long-term manufacturing partners. We specialise in customised tooling design and manufacture according to our customers’ specifications. Our staff have extensive experience in the rubber industry, providing you with high quality, professionally produced products. No job is too small or too big.


Hennig Gasket and Seals. (n.d.). Understanding Gasket Material Hardness. Retrieved 10 19, 2020, from Hennig Gasket and Seals: