There are basically 3 methods for PUR foaming.

RIM-process (reaction injection moulding) polyurethane is foamed to PU-compact and PU-integral skin foam. Application examples are: housing parts, dashboards, armrests.
SRIM-process (structural moulding reaction injection moulding) a glass-fibre mat is placed in the mould and is foamed around with a polyurethane hard foam. This technique is mostly used for interior linings or dashboards of coaches.
RRIM-process short glass fibres are blended with polyurethane constituents and injected in to the mould. Application examples are:for resistant bumpers.

The most common of the 3 is the RIM-process.
The plastics used are thermosets, like polyurethanes or foamed polyurethanes.
With the low viscosity and low injection pressures, large, complex parts can be produced more economically in low quantities.
Considerable design freedom is possible, including thick and thin wall sections that are not good for injection molding, due to the uniform shrink characteristics. Foamed polyurethanes are natural thermal and acoustic insulators.
Reaction injection molding is used in many industries for many types of parts. While bumpers for vehicles are produced in this process, most applications are for large, complex parts produced in quantities less than 10,000 units. Examples include panels, enclosures, and housings.

[ut_blockquote_right] In some occasions as much as 70% savings can be achieved on tool cost when choosing a PUR process over a standard injection molding process. [/ut_blockquote_right]

PUR Advantages

• Thick, light weight structural parts can be molded without sink
• Walls can be thick and thin on same part
• Tolerances approximate to Injection Molding
• Can mold over metal, glass, wood, wiring, circuit boards, hardware, etc
• Much better economies for lower volume parts

Injection Molding Advantages

• Part cost lower in high volume
• Plastic part can be colored; no need for paint
• Finer part detail can be achieved
• Greater range of material choices

Good luck and remember that there are often more than one way to get the result you are looking for.
Contact us at The Tool Hub and we will gladly help you with your project.