How Much Compression Do Rubber Gaskets Require?

Why Compression Matters

Rubber gaskets seal by creating a barrier under load. When rubber is compressed between two surfaces, it pushes back with a counterforce. Known as compressive stress, this counterforce fills surface irregularities, maintains contact pressure, and prevents fluid migration.

Compression is expressed as a percentage of the gasket’s original thickness. In other words, it indicates how much of the gasket’s original thickness is reduced when the rubber is squeezed between two surfaces.

If the compression is too low, the gasket can’t generate enough sealing force. If the compression is too high, the gasket may deform permanently and fail to bounce back to its original size when the compressive force is removed. In other words, the gasket reaches permanent compression set.

Solid Rubber Gaskets

Solid rubber gaskets require higher compression percentages because they don’t contain readily-compressible air pockets, or cells, like sponge rubber gaskets do.  Solid rubber and sponge rubber are both elastomers, but the presence or absence of a cellular structure is a key difference.

Typical Compression Range for Solid Rubber

• 20–30% compression is recommended for most solid rubber materials
• 15% minimum is required to achieve a reliable seal
• Above 35% risks over‑compression and permanent deformation

Elasticity and Durometer in Solid Rubber

Elasticity is a material’s ability to stretch or deform under load and then return to its original shape once the load (such as a closed door) is removed.  With gaskets, elasticity is what allows the rubber to rebound, maintain its sealing force, and recover after compression.

With solid rubber gaskets, the elastomer’s durometer or hardness affects its elasticity. More specifically, durometer measures how resistant a rubber is to indentation. It directly affects:

• Required compression force
• Ability to conform to surface irregularities
• Long‑term sealing stability
• Risk of permanent compression set

Soft, Medium, and Hard Rubber

The solid rubber materials that Elasto Proxy fabricates into gaskets have durometers that are measured on the Shore A scale. Depending on the durometer, a gasket material can be described as soft, medium, or hard.

• 40–50 Shore A: Soft, conforms easily, seals with lower bolt load
• 60–70 Shore A: Medium hardness, common for industrial gaskets
• 70–80 Shore A: Harder materials for high‑pressure or high‑temperature sealing

Compression Recommendations by Durometer

Durometer affects the amount of compression to apply to a solid rubber gasket. It’s not the only consideration, but it’s an important one.

• 40–50 Shore A: 20–25% compression
• 60 Shore A: 25–30% compression
• 70 Shore A: 30–35% compression
• 80 Shore A: 35% maximum (risk of compression set increases)

Harder materials require higher compression percentages to generate sealing force; however, harder materials also reach the limit of safe compression more quickly.

Sponge Rubber Gaskets

Sponge rubber gaskets contain tiny air pockets, or cells, that are either open or closed. Open cells allow fluids (including air) to pass between pockets. Closed cells do not. That’s why closed-cell sponge rubber is a better choice for water sealing.

When a sponge rubber gasket is compressed, its cellular structure allows the gasket to conform to surfaces with less force than a solid rubber gasket would require. However, because sponge rubber is less dense, more compression is needed to achieve a reliable environmental seal.

Typical Compression Range for Sponge Rubber

• 30–50% compression is standard for most closed‑cell sponge materials
• 50–60% may be required for soft open‑cell foams, cellular rubbers that are like sponge rubber but manufactured using a different process  
• Above 60% risks crushing cells and losing resilience

Closed‑Cell vs. Open‑Cell

There are also compression differences to consider between closed-cell and open-cell sponge.

• Closed‑cell sponge: Best for water sealing; compress 30–40%
• Open‑cell sponge: Best for air/dust sealing; compress 40–60%

Tip: When comparing sponge rubber materials, remember that closed cells don’t require as much compression and are better at maintaining their sealing force under load.