Urethane is a popular kind of resin used to develop various plastic components. The plastics are usually rigid, but Urethane is also used to create rubbery items that are much flexible. Urethane casting is almost similar to injection molding, but it uses soft tooling instead of metal. It’s the process of manufacturing small and low-volume products which are high quality and have a great surface finish. The manufacturer pours Urethane into a mold and allows it to cure for part formation. In this article, we point out some facts about Urethane resin.

Essential Facts About Urethane Resin

Urethane has excellent benefits in the casting process, considering the quality of the part of models created is unmatched. It’s perfect for creating intricate designs at a very low cost, unlike other production methods. Despite the advantages, there are factors associated with Urethane resin that can affect your end product either positively or negatively. They are;

1. Urethane resin is prone to shrinkage

Like in injection molding, where the liquid matter solidifies to form a mold, this is true for Urethane. During the final stages of the Urethane casting process, the resin is poured into a mold, cured for at least an hour or depending on the manufacturer’s instructions. As it cures, it changes from liquid to solid and takes the shape of the mold, which represents the final part. It loses volume of about 0.15 percent. It’s one of the things you must remember when creating a mold to ensure it’s neither too big nor small.

2. Urethane resin is affected by moisture

The resin is usually packed in airtight bottles to prevent any contact with moisture. After buying and opening the cap, make sure to put it back on immediately after pouring. Urethane reacts to moisture, especially that in the air. The reaction changes its composition and doesn’t work as well as before. You should take good care of Urethane resin to maintain its condition and avoid messing it up, forcing you to discard it

3. Urethane reaction produces heat

It is also referred to as an exothermic reaction. During the curing process, heat is released into the mold, affecting the rate at which the various parts cure. In the mold, Urethane may be more concentrated in some areas compared to others. Curing is fast in regions with a high volume of urethane resin, while it’s slower in the less concentrated parts. Due to the different curing times, following the recommended curing period is vital so that the part dries well.

4. The Urethane base color affects the tint

When painting a surface, in most cases, you expect the topcoat to remain as is and not change due to the base color. However, for urethane resin, be prepared for a different-looking color than what you bought. The primary base color of Urethane is white, but it can be colored, translucent or black. Tinting is okay, but it’s best to paint using the same color to prevent the color change.


Urethane resin varies from one brand to the other. Learn each type before starting the casting process. Also, consider the factors above before part creation to ensure the mold is the right size and the part is well dried and has a smooth finish. Keep all Urethane bottles covered to prevent moisture reactions and make them last longer.


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