Types of Shore hardness in silicone casting rubber

We have a wide range of different types of silicone casting rubbers in different Shores. The Shore hardness of silicone rubber has a direct impact on its properties such as flexibility, durability, and resistance to wear and tear. In this article you can read all about the different types of silicone casting rubber.

What is silicone casting rubber?

Silicone casting rubber is used to make flexible moulds for copying objects. Once the mould is made, it can be cast with epoxy, polyester, polyurethane, plaster, concrete, etc. Due to its flexibility and self-dissolving properties, the material is also great for copying fine details. The existing object is copied exactly.

What types of silicone casting rubber are there?

The silicones are available in different mates of flexibility (Shore) and we have 2 varieties: silicone casting rubber with a 1:1 mixing ratio and silicone casting rubber with a 10:1 mixing ratio.

Silicone casting rubber Shore 8

Shore 8 is the softest and most flexible silicone in our range. This Shore is used for moulds with difficult to release shapes. In addition, this silicone is very suitable for use in the erotic industry. The mixing ratio is 1:1 by weight.

Silicone casting rubber Shore 15

Shore 15 is most commonly used for Resin Art moulds. This casting rubber is flexible, easy to use and has a low viscosity. This makes this casting rubber very suitable for making epoxy moulds. We have Shore 15 in two types: 1:1 mixing ratio and 10:1 mixing ratio. We explain the differences further in this article.

Silicone casting rubber Shore 25

If you are looking for a slightly flexible silicone, you can use Shore 25. This is suitable for making silicone moulds with medium detailing. Because this silicone is just a bit stronger than Shore 15, it is also suitable for making concrete moulds. The mixing ratio is 1:1 by weight.

Silicone casting rubber Shore 40

Shore 40 is a hard silicone that is the least flexible of all types. This silicone is perfect to use for making large moulds or concrete moulds. We have this silicone in a 1:1 mixing ratio and 10:1 mixing ratio.

1:1 and 10:1 mixing ratio

Of Shore 15 and Shore 40, we have 2 types. In terms of properties after curing, they are very similar, but these are the properties of both:

Casting rubber 1:1

  • Processing time of 10 minutes.
  • Shore 15 is blue and Shore 40 is black.
  • Mixing ratio of 1:1 by weight.
  • Temperature resistant 200°C long-term and 300°C short-term.
  • Food safe.

Casting rubber 10:1

  • Processing time of 2 hours.
  • Translucent, colorable with pigment.
  • Mixing ratio 10:1 by weight.
  • Temperature resistant 250°C long-term and 350°C short-term.
  • Food safe.


We have silicone oil and a thickener for silicone in our range. These are additives for in the silicone casting rubber.

Silicone oil increases the Shore/hardness by about 1 point, thus making the current silicone a little softer and more flexible. Add up to 15% to the casting rubber.

Silicone thickening agent thickens the silicone casting rubber. Just add 1-3% to the casting rubber. This agent can also be applied vertically. In the video below you can see how Kees applies the thickener!


More information about silicone rubber?

Do you have questions about using silicone rubber? Feel free to contact our specialists. We will be happy to give you advice to make your project a success! Send us a WhatsApp message, send an email to support@polyestershoppen.com or call +31 85 022 0090 for free advice without obligation.

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Products used in this article

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