The Best Rubber Material for a Mold

The making of rubber molds throws up three different options of latex, silicone and polyurethane rubber. Understanding the properties and usage will help in choosing the right rubber for a project.

When it comes to making rubber molds, there are various options, from the natural latex rubber to synthetic compounds like polyurethane rubber and silicone rubber.

One of the first steps when making a mold will be deciding which rubber to use. While each has their own strengths and weaknesses, the choice will determine the process ahead. Let us take a look at each option –


Latex rubber is one of the least expensive mold making materials. Yet, it is very flexible, strong, durable, tough and tear resistant. It also captures minute details very well. As the rubber is viscous enough to not run off vertical surfaces, it can be applied to models such as architectural details where they are, without needing to be thickened.

Latex molds can be used to cast plaster, polyester resin, urethane or even abrasive materials like concrete. The molds can be used again and again to produce multiple castings. They will literally last forever as long as they are stored properly.

However, it takes a long time (around 10 to 15 days) to make a latex mold. It involves brushing multiple layers of latex on the model, while allowing sufficient time in between for every layer to dry properly.

The rubber works well for creating masks too. Moreover, liquid latex is a theatrical and special effects product used to create wrinkles, scars, gashes and as an adhesive for bald caps.In a less viscous form, the same material will work for casting purposes as a latex casting rubber too.


This is a high strength rubber with excellent chemical resistance. It opens up options of varying consistencies and even a choice of firmness for the mold – from soft to medium to hard. The cost is on the average side – neither too expensive nor very cheap.

Polyurethane rubber molds are most suitable for casting polyurethane, epoxy and polyester resins. The method of making the mold is not limited to brushing or spraying; polyurethane rubber can even be poured to make solid cube molds. The mold will be ready in a few hours or a day at best.

However, polyurethane molds are not as long lasting and can even lose their shape over time.


This is an expensive material, but the superlative properties and ease of use justify the price. It is a versatile, durable and highly resistant rubber with two types of catalysts – tin and platinum – that will affect its working and usage.

The rubber is formulated in varied types with food safe and skin safe options also available. The translucent variant can perfectly duplicate skin surfaces. The best part is that silicone does not stick to anything but itself, negating the use of a release agent.

Silicone rubber can be used to cast different types of materials except itself. Again, the same rubber can be used to make castings too.

Consider all factors of mold making to make the right choice between liquid latex, polyurethane and silicone rubber.

Types of Silicone Rubber

There are many basic differences between liquid silicone rubber, room temperature vulcanizing silicone and the high temperature vulcanizing variant which influences their potential use.

Silicone rubber is a man-made elastomer that is composed of silicone with carbon, hydrogen and oxygen. This inorganic rubber-like material is used extensively across various industries - rail, aerospace, automotive, food/beverage and artworks to name a few. The superior benefits of resistance to high temperatures, weather and abrasion coupled with chemical stability and electrical insulation make it a popular and commonly-used rubber for varied applications.

It is manufactured in three different forms with varying viscosity and curing temperatures:

  • Liquid Silicone Rubber (LSR) – As the name goes, this is in liquid form with good viscosity and flows well. It is a two-part silicone and the curing occurs only when the base material comes in contact with the catalyst. This is a thermosetting material and cannot be restored to its original form after curing. The range of hardness is wide, from 5 to 90 Shore A. The excellent liquidity ensures that the rubber can easily fill the most complex parts of the mold, making it perfect for automated injection molding, compression molding, transfer molding and other molds that have complicated designs or demand tolerance.
  • Room Temperature Vulcanizing Silicone Rubber (RTV) – This rubber is also in liquid state, but comes in both one-part and two-part formulations. The two-part variant is again of two types - condensation cure and addition cure. The former uses tin salts as a catalyst while the latter relies on a platinum-based catalyst to turn the liquid silicone into a solid form. It should be noted that these types of RTV silicone rubbers are not only quite different from each other, but also not even compatible with each other. However, all RTVs will cure at room temperature when they come into contact with air.

In general, RTVs cure to a soft or medium hard finish ranging from 15 to 40 Shore A. They have low shrinkage and can capture details well, making them suitable for injection molding, gravity casting and vacuum casting. They enjoy varied applications including mold making, casting, prototype-making, prosthetics and encapsulation. The tin-cured silicones have food safe, skin safe and transparent versions too.

High-Temperature Vulcanizing Silicone Rubber (HTV) –
This is also known as Solid, Milliable or High Consistency Silicone Rubber. It is usually in the form of solid, gummy rubber blocks which are partly vulcanized, though liquid forms are also formulated. It goes without saying that the rubber has to be heat-cured at high temperatures to get the finished product. It is used for compression and resin-transfer. Silicone tubing and other shapes are often extruded from HTV silicone rubber.

EnvironMolds offers a great selection of high quality RTV silicone mold rubbers that can be used to make a silicone mold or cast. This popular art supplier also provides skin-safe, food-safe and translucent silicone rubber formulations. Apart from this, other related materials, supplies, tools and equipment are also available.