What Is Shore Hardness (Shore A) and How It Affects a Seal
One of the most frequently asked technical parameters when ordering a rubber product is hardness. Hardness is usually expressed on the Shore A scale and directly determines how well a seal will seal and how long it will last. In this article we explain in simple terms what Shore hardness is and why it matters.
What is Shore hardness
Shore hardness is an indicator that measures how far a needle (indenter) applied to the surface of a material penetrates into the material. The measurement is carried out with a device called a durometer. The result is expressed as a number from 0 to 100: the higher the number, the harder the material. For example, 40 Shore A means soft rubber, while 80 Shore A means fairly hard rubber.
Shore A and other scales
Different scales are used for different hardness ranges:
- Shore A — for soft and medium-hardness elastomers (most seals are on this scale).
- Shore D — for hard plastics and very hard rubbers.
- Shore 00 — for very soft gels and foams.
The vast majority of industrial seals are in the 40–90 Shore A range.
How hardness affects seal performance
Choosing the right hardness is the key to successful sealing:
- Soft rubber (40–55 Shore A) — compresses well with little force, conforms well to rough surfaces, ideal for grooves with complex shapes.
- Medium hardness (60–70 Shore A) — provides a balance between sealing and strength; it is the most commonly used range.
- Hard rubber (75–90 Shore A) — withstands high pressure, reduces the risk of extrusion (being squeezed into a gap), but requires more compression force for a good seal.
How hardness is adjusted
The hardness of rubber is mainly determined by the composition of the compound. By increasing the amount of fillers (especially carbon black), hardness can be raised, while adding a plasticizer softens it. This makes it possible to obtain a wide range of hardness from the same rubber base.
How to choose the right hardness
When choosing hardness, you need to take into account the pressure, surface quality and installation gap. In high-pressure systems a harder material is preferred, while in places requiring precise sealing a softer material is preferred. To match hardness with the right type of material, it is useful to familiarize yourself with the basics of elastomers. Every measurement is checked in our laboratory as part of quality control.
If you are not sure which hardness is suitable for your project, see our products or contact our specialists — let us help you make the right choice.