Resin Transfer Moulding (RTM) – Methods, Benefits and Applications

Topics Covered

Resin Transfer Moulding Process
Companies Involved in Resin Transfer Moulding


Resin transfer moulding (RTM) is an increasingly common form of moulding, using liquid composites.

It is primarily used to mold components with large surface areas, complex shapes and smooth finishes. RTM is unlike reaction injection moulding and structural reaction injection moulding processes (SRIM), in which the chemical reaction is induced by the mixture of reactants.

Instead,  the chemical reaction for resins used in RTM are thermally activated from the fiber mat or preform and mold wall. The reaction speed of RTM is much slower than that in SRIM, allowing for a longer fill time at lower injection pressure.

Final RTM products will be light in weight and high in strength. However, RTM uses heavy structured tooling to withstand the hydraulic pressure, and hence it has high tooling cost.

Resin Transfer Moulding Process

RTM is a closed-mold, vacuum-assisted process that employs a flexible solid counter tool used for the B-side surface compression. This process yields excellent strength-to-weight characteristics, high glass-to-resin ratiso and increased laminate compression.

In this process, fiber preform or dry fiber reinforcement is packed into a mold cavity that has the shape of the desired part. The mold is then closed and clamped.

Catalyzed, low viscosity resin is then pumped into the mold under pressure, displacing the air at the edges, until the mold is filled.

After the fill cycle, the cure cycle starts during which the mold is heated, and the resin polymerizes to become rigid plastic. Gel coats may be used to provide a high-quality, durable finished product.

This process is well-suited for mass production of 100 to 10,000 units/year of high-quality composite fiberglass or fiber-reinforced plastic parts. It is recommended for products that require high strength-to-weight requirements. Tooling used in this process can be made from various materials including aluminum, nickel shell, mild steel and polyester.

The light RTM (LRTM) process, on the other hand, is similar to that of RTM, but differs in the method of closing the mould. The closure of the mould is done mechanically or by applying vacuum between two seals in the mould peripheral flange.

Companies Involved in Resin Transfer Moulding

The following is a list of various composite/fiber glass producers, specializing in RTM, with a brief introduction of their products:

  • Composite Integration Ltd is involved in providing market-leading, innovative, and well-engineered solutions to the composites industry. The company is a specialist in designing and manufacturing tooling for resin transfer moulding processes. It provides physical assistance in areas such as tooling design, materials selection, product design optimization, injection equipment, process control and training.
  • JHM Technologies was founded in 1990 with an aim to produce RTM injection equipment that provides the highest level of process control. It offers three types of tooling structure to satisfy all levels of production needs. The first level is a “BASIC” level developed with latest flow channel details to achieve uniform resin flow 360° around the mold perimeter and fitted with replaceable tubes or automatic injection ports. The second level is the “MAGNA” series which is added with conventional vinyl ester tooling gel-coat for improved durability in addition all key design details of the BASIC level. The third level is the “CONDITIONED MAGNA” provided internal 3/8" copper water lines to maintain the optimum tool temperature during injection and curing process.
  • Owens Corning, a market-leading innovator, in glass fiber technology was founded in 1938 and is one among the Fortune® 500 company for 58 years. Their product range for RTM include Multimat® product, Unifilo® U813, U816, U850, U852, U614 chemically bonded continuous filament mats, Uniconform® mat and Glass veils ECR20A and ECR70A.
  • Apogee Products, a specialist in hand laminating and fiberglass repair business, has produced high quality, low cost mould sets for fiberglass components of all shapes and sizes from small and intricate parts to campervan doors and truck-scale panels.
  • FormaShape has been a pioneer in the application and advancement of the LRTM process. Their product range includes SilkTekTM gas pump shrouds, SilkTekTM column cladding, SilkTekTM Signage, FormaStoneTM textured architectural panels, just to name a few.


The key benefits of resin transfer moulding include the following:

  • Good surface quality
  • Wide range of reinforcements
  • Large, complex shapes
  • Dimensional tolerances
  • Low capital investment
  • Less material wastage
  • Tooling flexibility
  • Low environmental impact
  • Labor savings
  • Ability to add inserts and reinforcements at a point of infusion for greater strength
  • Zero air entrapment within the product.


RTM is of major interest for various moulding applications as it promises performance improvements and cost savings over traditional methods. Some of the major applications of the RTM process include:

  • Truck panels
  • Boat hulls
  • Wind turbine blades
  • Aerospace and automobile parts
  • Medical composites
  • Bathroom fixtures, car body, helmet, etc.


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