Making Body Molds with Silicone Rubber

Think body molds; think alginates! Indeed, alginate is the material of choice for capturing molds from the live human body as it is completely safe for the skin. This natural organic material sets quickly and the level of detail is also superior.

However, alginate comes with its own set of drawbacks. For instance, alginate can easily tear during demolding. Even if you manage to demold properly, the molds tend to shrink on contact with air as the water evaporates. They will start losing details within a few hours itself and are mostly unusable after 24 hours or so. Therefore, you have to cast them quickly; within an hour or two at best. Again, these are waste molds as you cannot even consider using them for making multiple castings.

Moreover, you cannot cast resins or polyurethanes in alginate molds. They are mostly suitable for plaster casting only.

Another option

Not many people may be aware that silicone rubber can also be used for making body molds! Indeed, skin-safe silicone is available in the market and LifeRite Skin Safe Silicone from the house of EnvironMolds is a good option.

This 2-part RTV silicone rubber is suitable for life casting and can be easily sourced from The body molds will turn out tear-resistant and have a long life.

They can be used again and again for making resin, polyurethane or plaster casting, making it possible to replicate multiple copies using the very same mold!

Multi-Purpose Nature of Sodium Silicate

I recently came across water glass – also called liquid glass – on the EnvironMolds website I am well aware that sodium carbonate and silicon dioxide react when molten to form sodium silicate and release carbon dioxide. This compound is regularly used in cements, passive fire protection, refractories, textile and lumber processing, and automobiles.

Imagine my surprise when it dawned on me that the same sodium silicate also enjoys patronage in the world of mold making and casting! The potential of sodium silicate in working as an effective deflocculant for clay slips is still understandable.

However, I had no clue that this same compound would help provide an antique finish to ceramics! All you have to do is brush a thrown pot with a solution of sodium silicate. The painted surface is then quickly dried before expanding the pot from inside. What happens is that the thin skin of sodium silicate first hardens when dried with a blow torch or heat gun while the clay still stays soft and malleable. The pressure of expansion from inside cracks the skin to give the pot an instant antique look. The glazed surface looks quite authentic.

EnvironMolds offers Sodium Silicate in aqueous solution that can be used for ceramics, metal mold making, cement and plaster sealing and also as a high temperature adhesive. It is odorless, non-toxic, moisture resistant, non-flammable and comes at a very low cost too.

Alginate Safe for Skin Contact

Alginate is the most commonly used material for making body molds. As it is extracted from seaweed and combined with other harmless substances, alginate can be safely applied on any part of the human body.

In fact, alginate is a natural organic material that is food safe as well. It is used as an ingredient in many food products and is safe to eat. Alginate is also regularly used to capture dental impressions and life casting alginate has evolved from this formula itself. The mold making version is only modified to deliver slower setting times.

All you have to do is mix the alginate powder with water to form a gel like paste. Avoid using hard water for this purpose. The alginate paste can be easily applied on the face, hands, legs, torso or the entire human body too. It will set within a couple of minutes and can be easily demolded by twisting or wriggling the body part.

EnvironMolds provides a range of alginate formulas that capture incredible details and provide an exact reproduction of the body part where it is applied. Apart from the traditional formulas, there is a silica-free version (softer set suitable for babies and small children) and fiber-reinforced version (delayed shrinkage and improved tear strength for larger molds). Check for other slower set variations as well.

Of Reusable Mold Making Materials

Regular mold making materials such as clay, alginate, plaster bandages, silicone rubber and polyurethane rubber are good for single use. In other words, you can use them to make a mold once and that is it. While clay, silicone or polyurethane molds can be used multiple times, the material itself cannot be used again to form a new mold.

Perhaps the only reusable mold making material is thermoset mold rubber!

Thermoset mold rubber comes in a box and has to be heated (in a microwave) until it melts completely. Now the molten rubber is directly poured into the mold box to completely cover the model. That’s it, no measuring or mixing is required. It gradually hardens on cooling, and soon a flexible rubber mold is ready for use.

The mold made can be repeatedly used to produce multiple casts without any noticeable degradation whatsoever. And once you are finally done using the thermoset rubber mold, it can easily be melted and reused to make new molds quite effectively. In fact, some thermoset mold rubbers such as Wizbe’s Composi-Mold can be re-melted and reused as many as 35 times!

Three variants of Composi-Mold are available at EnvironMolds website
  • Composi-Mold-LT - a soft flexible rubber which sets similar to a Shore A 10.
  • Composi-Mold-PowerMold - a firmer version for making two part or push molds with Shore A 25 hardness.
  • ComposiMold-FC - a FDA compliant food grade mold rubber.
In sum, thermoset mold rubber is an extremely cost-effective option over the regular polyurethanes for sure!