What does Shore A Hardness Mean?

Shore hardness scales are the way in which different materials are measured for their hardness – it allows people to accurately compare the relative hardness of different items, much as you might compare the temperature of something using a shared scale like Celsius or Fahrenheit. 

There are 12 Shore hardness scales, A, B, C, D, DO, E, M, O, OO, OOO, OOO-S, and R. The three commonly used scales for industrial products and components are: 

• Shore 00 – used to measure particularly soft substances, like soft rubbers and gels. 
• Shore A – used to measure flexible rubbers and some semi-rigid plastics. 
• Shore D – used to measure hard rubbers and plastics. 

Shore hardness scales take their name from Albert Ferdinand Shore, who first developed them in the 1920s. 

How is hardness measured? 

Hardness is measured by applying pressure to the material – typically either with an indenter (a pointed object) or a presser foot (a flatter object). These are forced into the material for a set amount of time, and with a defined amount of pressure using an instrument known as a durometer. The resulting effect on the material is measured, and applied to the scale to give a number out of 100 – the lower the number, the softer the material, and vice versa. 

Examples of products on the Shore A scale

To put all of that into perspective, here are some common items alongside their Shore A hardness rating: 

• Elastic band = 20 (soft) 
• Pencil eraser = 40 (medium soft) 
• Door seal = 55 (medium soft) 
• Rubber sheeting (used to manufacture seals, gaskets, O-rings, etc) = 68 (medium hard) 
• Car tire tread = 70 (medium hard) 
• Shoe heel = 80 (hard) 

As you can see, there is a huge range of materials covered by the ‘A’ range. Softer items like gel shoe insoles would be too far off the bottom of the range, and so fit on the ‘OO’ scale, and harder items like plastic hard hats would be too hard for this scale, and so sit on the ‘D' scale. 

Why is Shore Hardness important? 

The hardness of the materials used in various products is an extremely important factor – you would not want a skateboard wheel with the same relative hardness as an elastic band, for example, as it would not perform to expectations.  

For smaller components, like O-rings, gaskets and seals, for example, it is important to get the perfect amount of hardness – they need to be sufficiently hard to form the required seal without being brittle or completely inflexible. For this purpose, most of these products are manufactured from materials between 65 and 90 on the Shore A hardness scale for hydraulic use, and 65 – 75 for pneumatics. 

About First Mats 

At First Mats, we supply non-porous rubber sheeting with a Shore hardness of 68 – ideal for manufacturing seals and gaskets for various uses. Our sheeting is available in thicknesses from 1.5mm to 25mm, and can be supplied cut to length or on the roll. For more information, you can check out our full range of Rubber Sheeting here, or contact us using info@firstmats.co.uk.