Shore Hardness Guide

The hardness of materials, typically polymers, elastomers and rubbers, is measured on a Shore Hardness scale.

Shore Hardness scales measure the resistance of a material to indentation. The hardness of a material is tested using a durometer device. This measures the depth of an indentation in the material created by a given force on a standardised presser foot.

Image of durometer

This resulting number is rated on a scale known as the Shore Hardness scale or Durometer scale. The number on the scale indicates the materials resistance to indentation. A higher number indicates greater resistance to indentation so therefore a harder material. Softer materials are lower on the scale.

There are several scales of durometer used for materials with different properties, however in engineering plastics Shore A and Shore D are most commonly used.

Shore A

The Shore A scale is used for measuring the hardness of softer, more flexible materials. Shore A “0” denotes extremely soft, gel like materials such as silicones, while semi-rigid plastics will be measured at the highest end of the scale around 90-95A.

Typical properties and applications:

90 Shore A materials are suited to machining compared to softer materials that can be ground. Softer materials typically benefit from better elongation at break properties in comparison to their harder counterparts. Polyurethanes are most commonly used around the 80-95A shore hardness range due to a good balance of mechanical properties. They have enough flex to absorb impacts, whilst also being rigid enough to maintain their profile under pressure. Applications for this range include shock absorbers and soft touch over moulded parts.

Shore D

The Shore D scale is used for harder rubbers and plastics. There is a cross over between the A and D scale, with materials softer than 50D (approximately equivalent to 95A) expressed using the A scale. Any material harder than this follows the Shore D scale. Materials harder than 65D usually feel completely rigid and do not have the flexibility and surface flex of A scale grades. At the top end of the D scale, a transition is made to the Rockwell scale where materials such as Nylons and Acetals are found

Typical properties and applications:

Harder materials offer a much greater resistance to flex making them an ideal choice for applications such as impact protection and metal replacement. Applications include mechanical products such as gear wheels and cogs, and castors and wheels.

Typical hardnesses of typical engineering plastics:

Rubbers: 10A-90A
Polyurethanes: 35A-80D
TPEs: 10A-95A
Polypropylenes: 75D
Nylons: Rockwell R110
Acetal: Rockwell R120

Chart showing Shore hardness