Uneven sealing surfaces need a soft rubber gasket material that deforms to fill the space. Covers and enclosure doors are examples where the closed gap often varies. A soft material will seal better than one that’s firmer.
Gasket material softness is measured by durometer and expressed in terms of Shore A and D. Understanding this will help when it’s time to order soft rubber gasket material.
Shore Hardness Scales and Durometer
Rubber and plastic firmness is measured by pushing a hard point into the material and measuring the indentation. The measurement system used is the Shore hardness scale, named after its inventor, Albert Shore.
Shore’s indentation device is called a durometer. This is why rubber hardness is sometimes spoken of in terms of durometer, or “duro.”
As the hardness or rubbers and plastics varies widely, Shore defined several scales but for most practical purposes Shore A and Shore D are enough.
Shore A and D Values
Shore A covers softer materials, Shore D those that are firmer. Both scales run from 0 to 100. They overlap, so rather than specify the top end of the A scale it’s more usual to use the middle of the D scale.
Here are typical Shore values for common materials:
- Rubber band – 20 Shore A
- Pencil eraser – 55 Shore A
- Shoe soles – 70 Shore A
- Leather belt – 80 Shore A.
- Golf ball – 50 Shore D
- Shopping cart wheels – 60 Shore D.
Shore Values and Soft Rubber Gasket Material
The softest material generally used for gasket applications is 30 duro, or Shore A, neoprene. Slightly firmer neoprene, nitrile and EPDM are all available in 40 duro / Shore A.
Foam is usually softer than solid material, as the air pockets provide additional compressability. Open cell foam is softer than closed cell in the same material, but will let fluids through.
Advice on Soft Rubber Gasket Material
A soft, closed cell rubber material is better for sealing uneven surfaces like those on doors and covers. The firmness of these is usually specified in Shore A. Ask us for help in choosing the best material for your application.