Casting Foam in Polyurethane Rubber Molds

Use Silicone Rubber (if you have it available to you)

Ideally, silicone rubber molds should be used when casting polyurethane foam. Silicone is often preferred because release agent is not required during the casting process (adding a barrier coat or paint can extend mold life, however).


Primed Mold Foam Casting

 A silicone mold (TinSil® 80-30) being primed for foam casting.
Watch a foam casting tutorial (using a silicone mold) here:

Perhaps polyurethane rubber is all that you have in-stock, or you don’t want to spent the extra money on silicone rubber. There is a solution that will make your polyurethane rubber mold act like a silicone rubber mold: PolyCoat Semi-Permanent Sealer & Release Agent.


 PolyCoat Release & Sealer Polytek

 PolyCoat Semi-Permanent Sealer & Release Agent


Create a Silicone “Coating” on Polyurethane Rubber Molds

PolyCoat Semi-Permanent Sealer & Release Agent is a low-viscosity, silicone-based liquid that can be applied to cured polyurethane or silicone molds (it can also be applied to original models before pouring liquid rubber over them during the mold making process).

PolyCoat can be brushed or sprayed onto the mold (use a Sure Shot Atomizer for spraying). Once applied, it takes about 5 minutes for the solvent carrier to evaporate and about one hour to cure, leaving behind a thin coating of silicone. The cure time of PolyCoat will depend greatly on temperature and humidity of the workspace and may take longer than one hour.

When casting polyurethane foam, it is recommended to apply at least two to three layers of PolyCoat to the cured polyurethane mold. Ensure that each layer is thoroughly dry before applying the next layer.

Once PolyCoat has been applied to the polyurethane mold, there is no need use any additional release agent. This is especially advantageous if the cast foam parts need to be painted. Paint will not adhere to cast parts when release agent is present and removing release agent from castings can be difficult; the application of PolyCoat eliminates these painting issues. PolyCoat even allows the application of a barrier coat or paint (after PolyCoat has been applied and is cured) to increase mold life and produce pre-primed parts right out of the mold.


Internal Testing

Tests performed at Polytek have shown that over 100 rigid, pre-primed polyurethane foam castings can be made from a polyurethane mold (mold product: Poly 74-55) with a PolyCoat coating.


Decorative Foam Castings-01

This polyurethane mold (on the left), coated in PolyCoat, rendered all of these rigid foam castings


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3 Responses to “Casting Foam in Polyurethane Rubber Molds”

  1. Johan says:


    What’s the better suited silicon for flexible PU foam?
    What mold life span can I expect and do you have tips to extend it?



  2. Polytek Development Corp. says:

    Hello Johan –

    Relatively hard silicone rubbers (like PlatSil 73-40 are good options for casting flexible polyurethane foam. When constructed properly, upwards of 100 foam castings can be made in these molds. Applying a barrier coat to the mold (e.g., water-based primer) can help to extend mold life.

  3. Johan says:


    A 1% tooling cost is an interesting promise. Could you please send me an offer for a self skinning PU foam mold supply :
    – mold + coating (is it permanent?)
    – instructions for quality casting
    – durability tips (mold cleaning, resting time between casts, etc.)



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