Exclusively used in industrial production applications, urethane is a family of rubbers and plastics materials that are used for making molds. Urethane rubber is widely known for its tough properties, being abrasion-resistant, economical, relatively simple to mix and apply, and flexible once it is formed into a mold. The urethane rubber molds are then used in industrial design projects, such as sculpture replication or stamping designs into concrete. This makes urethane rubber one of the most economical mold rubber products ever to be utilized.

In the urethane family, urethane rubber is considered to be one of the more tensile, durable, and cheap materials to work with when compared to silicone. While silicone does not need a spray-on mold release agent, it is not as easily resistant to abrasion and is therefore used in more delicate casting processes. Not only does urethane rubber have a high tear strength, but it is reusable, retains its shape, and comes in a range of malleabilities.

When used in conjunction with sealant and a release agent, urethane rubber can be poured, brushed, and sprayed onto an assortment of hard materials for casting purposes. Urethane rubber develops a viscosity similar to water when in liquid form, making it easy to apply. In addition, it has good cohesion when mixed with other forms of urethane rubber and incorporates well with fibers and foams, resulting in a more textured mold when needed. One of the best-known brands of urethane rubber manufacturers is Smooth-On.

A typical casting of a sculpture, for example, proceeds as follows:

1. The model to be cast is sealed at least twice with a sealant. This is especially important for models of porous properties; stone, wood, or water- or sulfur-based clay sculptures would need to be coated. Allow hardening of the sealant layer before proceeding.


2. Apply a release agent to the sealed model.


3. Mix and apply the urethane rubber by either brushing, spraying, or pouring it on the model. If tweaks to the mold are necessary, they must be done before the urethane rubber hardens completely.


4. Demold by separating the urethane rubber mold from the model. A precise and accurate impression of the model should now be indented into the urethane rubber mold.


5. The resultant urethane rubber mold is now ready for reuse. Apply a release agent to the inside of it before casting additional models.