RIM vs Structural Foam

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RIM offers

Lower Tooling Costs

Lower Required Production Volumes

than Structural Foam
Since structural foam uses essentially the same process as regular thermoplastic injection molding, the advantages of using the Reaction Injection Molding process versus structural foam are similar.

Design Features

While structural foam molding is a great option for parts requiring thicker walls, only RIM gives the designer flexibility to produce parts with significant wall thickness variations – typically from 0.125″ to 1.125″ in the same part. RIM can also produce high strength large parts at a lower cost because mold pressures are significantly lower compared to that needed for structural foam.


Unlike structural foam molding, the low temperatures used in RIM allow materials to be safely encapsulated within a part. Antennas, metals, electronics, circuits and other features can be encapsulated to increase mass, strength, burst protection and branding of parts.

Finish & Surfacing

Structural foam parts have a similar finish quality as RIM parts, and both processes take paint, silk screening and texturing well for improved cosmetic branding.


While RIM is the more cost-effective option for low to medium volumes, structural foam molding can be used for higher volumes if its other benefits prove to be important. Neither process is the best for production of high volumes.

Lead Times

Exothermic uses in-house machining centers to drastically reduce processing and assembly time and create production molds within 4 weeks; this timing is typically faster than a structural foam mold can be created.

Tooling Costs

Since RIM molds can be machined from low-cost aluminum, the upfront tooling costs are lower than that of structural foam tooling. This is particularly beneficial when part volume is low. RIM tooling is also much easier to change and will be more cost-effective if there is a chance that features will be modified.

Other Design Benefits

The low molding pressures of RIM allow for addition of non-drafted features, side action and undercuts without additional cost. Because polyurethane is denser on the outer surface than the inner layers, RIM parts have a high strength to weight ratio.

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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