RIM Technology

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Reaction Injection Molding systems combine two liquid components that chemically react in a closed mold to form a polyurethane plastic part. Unlike processes which require very high temperatures and pressures to melt and force plastic into a steel tool, RIM molding is an exothermic process, and the reacting urethane expands within the mold filling the cavity without external pressure while using significantly less energy. Tools are machined out of aluminum for less expensive molds, shorter lead times, and greater flexibility in design and changes.

Features & Benefits

Design Freedom

RIM is often a great alternative for designers who want the mainstream look of molded parts but cannot justify the tooling costs and volumes of typical thermoplastic parts. With RIM, you can develop a sculpted, structural design that minimizes hardware and includes value-adding features, all at a price point that is cost-effective for low to mid-range volumes, especially for larger complicated parts.


RIM is an optimal choice for low to medium volume production. Because initial tooling investments are less than half the cost of an injection mold, short runs remain economically viable and allow companies to minimize inventory while the product’s market success is being evaluated. RIM molds are easier to machine, so design changes can be made quickly as needed, and the process is often a more economical choice compared to cast urethane molding.

Part Size

Because such low pressure is needed, RIM is one of the most cost-effective options for molding large parts. There are no upper size limitations, other than equipment capabilities, for part design in RIM. If additional strength is required, RIM parts can be reinforced with composite fibers or structural members.

Design Complexity

One of the most unique features of RIM molding involves the ability to produce parts with significant wall thickness variations – typically from 0.125″ to 1.125″ in the same part. This allows the designer much greater flexibility when it comes to optimizing designs to meet critical customer specifications.


Urethane RIM parts can be formulated to be highly durable, skid and mar resistant, and virtually unbreakable. Ribbing ensures large parts won’t “tin can” or show sink marks like those that can occur in other injection molding processes. RIM parts are also inherently chemically resistant and possess high impact strength.


The low molding pressures and temperatures of RIM allow even the most sensitive electronic boards and components to be encapsulated without damage. Due to the adhesive nature of the curing urethane, encapsulation allows one to easily increase strength, mass, and burst protection. RIM allows for a wide variety of materials to be encapsulated.


The surface finish of RIM molded parts can be painted to produce Class A surfaces. Silk screening can also be applied adding to the appearance and branding of the product’s design.

Reduced Risk

The low cost tooling investment of RIM reduces financial risk while decreasing lead times. Exothermic is able to bridge the gap between prototyping and production with tools that yield molded parts ready for finishing in nearly the same time it takes to make prototypes.  Our in-house, high speed HURCO machining centers allow us to build detailed molds often within 2 to 3 weeks. The low-pressure tools are economically modified, so design changes can be quickly implemented based on the product’s market success.

RIM Process

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