Reaction Injection Moulding (RIM), also known as low-pressure reactive injection molding, is a relatively newly developed process applied to producing rapid prototypes and low-volume rapid injection moulding products. 

It injects two polyurethane materials into the rapid mold at room temperature and low pressure. The products are formed through chemical and physical processes such as polymerization, cross-linking, and materials curing. 


Compared to other plastic manufacturing processes, RIM has several advantages.


Because the viscosity of the bi-component mixture injected into the mold is much lower than that of molten thermoplastic polymers. RIM parts are flexible, lightweight, and thin-walled. For making lightweight parts for prototyping and small-series production purposes, RIM is usually a perfect option, such as the trial production of car bumpers and grilles.

Non-uniform wall thicknesses

RIM parts can have non-uniform wall thicknesses. This feature is unique, compared to other plastic manufacturing processes, such as vacuum casting. It empowers engineers and designers with more design flexibility.


The mold cost for RIM is relatively lower. Also, the mixture mentioned above requires fewer clamping forces. As a result, smaller machines are needed, which means less investment. So the overall cost for RIM is lower than that of traditional plastic injection molding processes. 

Fast production times

As one of the rapid injection moulding processes, molds for RIM can be ready within weeks, thus decreasing the total turnaround time. Therefore, the production times are faster than plastic injection molding. It enables companies to bring their newly-developed products to market early, which keeps them competitive in the quick-changing market.

Other Facts

1. Molds for RIM

ABS molds (20-50 pcs), resin molds (50-500 pcs), aluminum alloy molds (500-5,000 pcs), and steel molds (10,000-50,000 pcs).

2. Materials for RIM

The material for RIM is called polyurethane, PU in short. It can be divided into three types.

· Foamed PU. They can be soft foam and dense foam, which are used to make sound insulation covers, heat insulation layers, etc.

· Micro-foaming PU. Its density is generally 0.6-0.7 kg/m³. They can be applied to thick-walled and high-strength products.

· Non-foaming PU. The material performance is similar to PP or ABS with a density of about 1.1-1.2 kg/m³. They are suitable for various thin-walled shell products, with aging resistance, strong impact resistance, high cohesion, easy to load and unload, etc.

3. Injection pressure of RIM

The injection pressure is about 10MPa with a flow rate of 600g/s.

4. General working time of RIM

Each part takes 15-30 minutes to make. The demoulding temperature is usually controlled below 40℃, and after demoulding the parts are cured in an 80℃ environment for 2-4 hours for best performance. The materials and the sizes of the product determine the curing time.

5. Standard tolerances of RIM

According to its structure, the wall thicknesses of the product are different and their tolerances vary as well. The tolerance is usually within ±0.20mm/100mm. By designing the tooling, the part can be processed a second time to ensure tolerances of the position with particularly high precision requirements.

6. Thickness of the part injected

3mm or more.

7. Maximum size of the parts

Up to 30 kg of weight and up to 2500x1500x1000 mm in size.

8. The process of RIM

Initially, the monomer or prepolymer is mixed in a liquid state with a metering pump at a certain ratio into the mixing head. After the mixture is injected into the mold, it reacts rapidly and is cross-linked and cured in the mold. Then, after demolding, the part is complete. Finally, the RIM parts will be post-finished. Nearly all surface treatments are available, including painting, plating, screen printing, hand transfer printing, etc.

This process can be simplified as follows: storage → metering → mixing → mold filling → curing → demolding → post-treatment.

9. Applications of RIM

As one of the low-volume rapid injection moulding manufacturing methods, RIM is widely used for small-batch production of car models and accessories, medical equipment shells, toys, digital products, home electronics, fitness equipment, etc. If you need to make large-sized plastic products, but the quantity did not reach the MOQ of injection molding, you can turn to rapid reaction injection moulding.

rapid reaction injection moulding automotive parts

To better understand RIM’s applications, let's look at the top three most commonly applied industries. 

  • Medical device industry 

    Shell production of medical carts, CTs, ophthalmic treatment instruments, medical B ultrasound devices, color ultrasound devices, reagent instruments, hematology analyzers, cell analyzers, virus detection instruments, tumor detection instruments, laser treatment instruments, environmental detection instruments, gas chromatographs, liquid chromatographs, beauty instruments, etc.


  • Automotive industry

    Production of bumpers, car dashboards, car door panels, side trim panels, modified cars, etc.


  • AI industry

    Shell production of service robots, industrial robots, etc.

10. RIM market is growing

The market for Reaction Injection Molding is growing, driven by increasing demand for lightweight, durable, and high-performance plastic parts in various industries, including automotive, aerospace, medical, and consumer goods. 

One of the key drivers of growth in the RIM market is the automotive industry, where RIM is increasingly being used to produce lightweight and high-strength components, such as bumpers, spoilers, and body panels. The aerospace industry is also a significant market for RIM, where it is used to produce lightweight and durable components for aircraft interiors and structural parts.

Another factor driving growth in the RIM market is the increasing adoption of RIM for medical applications, such as prosthetics, orthotics, and medical devices, due to its ability to produce complex shapes with high accuracy and excellent surface finish.

In addition, the RIM market is benefiting from technological advancements, such as 3D printing and computer-aided design (CAD), making it easier and more cost-effective to produce complex RIM parts.

11. How are RIM suppliers in China different from each other?

Production capacity

Some suppliers may have more extensive production facilities or more advanced equipment for rapid injection moulding, allowing them to produce larger quantities of parts or more complex ones than others.

Material expertise

Some suppliers may have more experience working with certain materials or producing parts with specific physical properties, such as high strength or flexibility.

Quality control

There are many quality standards and quality controls in the RIM industry. Different vendors employ different ones. ISO 9000:2015 certification is common for quality management. However, quality standards for prototyping and low-volume production vary from project to project. Common practices are that the supplier and customer agree with the quality standards using 2D files at the beginning of each project. Some suppliers may have stricter quality controls than others. They use their own SOP (Standard Operating Procedure) to avoid human errors to the greatest extent and ensure they can meet the required standards.


Different suppliers may have different pricing models, with some offering lower prices but perhaps sacrificing quality or lead times, while others may offer higher prices but with higher quality or faster turnaround times.

Customer service

Working with Chinese suppliers, language and time differences may be the top two barriers. Some suppliers may be less fluent in English, which might cause misunderstandings. Some may be not able to work in the customer's time zone. Both would result in unexpected bad results. So, choosing a vendor who can communicate smoothly with you and be responsive is very essential for a successful RIM project.

By doing some research, and requesting a free quote and a trial order, you can distinguish which rapid injection moulding supplier suits you the best.

As a low-volume rapid injection moulding manufacturer, X Rapid Technologies provides a one-stop RIM service. Feel free to get in touch with us and discuss your requirements. You will get free quotes within 24 hours and kick-start your projects soon.