RIM vs Cast Urethane

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RIM offers

Unlimited Mold Life

Significantly Lower Cost, Stronger Parts

than Cast Urethane

Design Features

Both processes offer a good deal of design freedom, including the ability to mold in features and encapsulate materials. They differ in the fact that only RIM allows for part design with significant wall thickness variations – typically from 0.125″ to 1.125″ in the same part.


Both RIM and urethane casting can be used to encapsulate a variety of materials, from metals to electronics.

Finish & Surfacing

Both processes produce a high quality finish, but also take paint, silk screening and texturing well for improved branding. RIM Molded parts are typically stronger and more accurate.


Urethane casting into rubber molds is often the more cost-effective choice for small production volumes under 25 pieces. Silicon Rubber molds typically last for 25 cycles, however the part quality over the life of the rubber mold deteriorates as the mold wears. Using rubber molds for long-term production is very expensive compared to RIM Molding. Machined aluminum RIM molds simply don’t wear out and end up saving in the long run.

Lead Times

Both processes are appropriate for producing molds for quick turnaround.

Tooling Costs

The initial tooling costs of urethane casting are lower than that of RIM. Tooling modification in RIM is also very cost-effective, and when aiming for production parts, RIM becomes the better choice.

Other Design Benefits

Many companies utilize urethane molds for years prior to converting to more permanent tooling, which can end up being extremely expensive. Because RIM can bridge the gap between prototype and production with parts that are molded instead of fabricated, it can actually be most cost effective to utilize RIM in lieu of rubber molding.

Though these are some of the main considerations to account for when deciding on a production process, there are many issues to balance when determining the most effective option. Let Exothermic help you uncover the opportunities for success and guide your design concept to meet those process needs.

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