The RTM (Resin Transfer Molding) process is an abbreviation for the resin transfer molding process. The working principle is as follows: pre-reinforcement material is placed in the cavity formed by the upper and lower molds. After the mold is closed, the resin glue is injected into the mold cavity with a special pressure device. After the reinforcing material is impregnated, the product is cured and released.

In this process, how to effectively wet out the resin with the reinforcing material is the most critical step. If the impregnation occurs badly in the middle, the product will be scrapped. In addition to considering the viscosity, gelation time and other factors in the choice of resin, how to improve the conductivity of the reinforced material has also become the direction of everyone's research, and infusion mat was born.

Normally there are three layers: the upper and lower surface layers are glass fiber chopped strand, and the middle is a PP material flow felt, which is bundled together by a polyester thread to become a sandwich structure. Therefore, infusion mat is also called sandwich mat. Among them, chopped strands are used as reinforcing materials to provide strength; PP felts are used for rapid flow guidance during resin introduction.

The use of infusion mat in the RTM process has the following advantages:
1 easy to cover, can adapt to different shapes of products;
2 The product combination method uses a bundling line, does not contain a chemical binder, has good compatibility with the resin, and is resistant to erosion and does not easily wrinkle;
3 The fiber content is stable, which can ensure the stability of the product;
4 Due to the presence of the PP diversion layer, the resin's flow and permeability are better;
5 According to the different thickness of the product, there are a variety of combinations to reduce the ply.

Although the infusion mat has many advantages, when used alone, the strength is poor, and it is generally used together with an axial cloth or a composite felt according to the requirements of the product.

In order to solve the problem of weak strength, in fact, there are other combinations, such as changing one layer of chopped strand into roving in 0 and 90 degree. With continuous fibers, there is a significant increase in strength.