Shore hardness is a measure of how hard a material is, it is measured with a durometer and higher numbers indicated harder materials. There are several different scales, but for silicones, polyurethanes and resins etc. we use the 00, A and D scales.

• These scales have values between 0 and 100.

• We denote which scale by appending the scale type to the value. Ie. 00-10, 15A, 75D

• 00 is used to measure very soft materials

• A is used to measure soft materials

• D is used to measure hard materials (like plastics)

• These scales overlap, with 00-44 = 0A and ~62A = 0D.

What does this mean for mould making and casting?

Shore hardness is an important factor in material choice when mould making or casting finished products.

In most cases, the major consideration we should always be thinking about is -

• How hard will it be to get out of the mould?

• How hard will it be to get the original piece out?

If you’re moulding just a simple small box shaped object with no overhangs or intricate designs, then it doesn’t particularly matter if your silicone is 0A or 45A. As both will be able to be removed from around the original object.

If you are casting a complicated geometry like a hand model, then you would want to work with a softer silicone that would be easier to remove from a given mould. If you went with a 70A silicone, it would be near impossible to remove the casting from the mould and even if you were able to get the piece out it would likely be damaged from the force required.

What is the best shore hardness for general moulding?

We believe that for most casting and moulding applications a shore hardness of around 15-25A will work best. In this range the silicone or polymer will be flexible enough to remove easily from moulds but also firm enough to retain structure as a mould. The unmixed silicones are of a low enough viscosity to be able to be mixed easily. If you have never used silicones before then these are probably were you want to start.

We have 2 silicones in this shore hardness range.

• 15A (recommended overall) - 15A Link

• 20A (quick set) - 20A Fast Link

We have a wide range of silicones in different shore hardnesses, for all sorts of different applications, check out the table to quickly compare shore hardnesses. All are food grade and skin safe.