The fabric is placed in a mold and then resin is infused, until its complete saturation. The process is repeated with multiple fabric sheets, according to the required mechanical properties.
Afterwards, the structure is placed in an environment with normal atmospheric conditions, until hardening of the resin is completed.
Note that before the first fabric layer, the mold may be coated with a sheet of gel coat, which will form the outer surface of the structure.

The fabrics are placed in a mold and impregnated with resin, in the same way as with the Wet Lay-up method. Afterwards, vacuum pressure is applied so as to enable better homogenization of the material.
Vacuum pressure is implied successfully through sealing with a special vacuum bag and the removal of air by using a vacuum pump.

The vacuum resin infusion is a product manufacturing process of composite materials by using a closed mold.

The system, being in vacuum, absorbs the resin until the complete saturation of the filament reinforcement.
It should be noted that this particular method, governed by the Darcy law, is absolutely controllable. The factors which are affecting this method are (a) the filament reinforcement, (b) the viscosity of the polymer and (c) the differential pressure between the atmosphere and the system.

Provided that during the process these parameters remain stable, the method ensures the required results. Last but not least, vacuum infusion is environmentally friendly, because during the process the system does not come into contact with the atmosphere.

The LRTM - Light Resin Transfer Molding method uses two molds. The first one is used as a base and is covered with fabric and the second one, being flexible, seals the base by creating a closed system of two molds. Afterwards, with or without the use of a pump to transfer the resin, the saturation of the filament reinforcement is successfully completed.

This process ensures:

• High productivity
• Reduced labor costs
• Smooth surface on both sides
• High geometrical integrity
• Absolute control of the process
• Stable mechanical properties
• Long mold life
• Environmental friendliness

In this method pre-impregnated (prepreg) fabrics which contain a certain percentage of resin are used.
After being placed onto the mold with the appropriate technique, they are sealed, and the structure is put in the Autoclave.
By applying pressure in the oven chamber, vacuum to the system (structure with the two molds) and high temperature, the polymerization of the resin is ensured in a controllable manner, resulting in upgraded mechanical properties.

This method is similar to the Autoclave method, with the difference that there is no use of positive pressure on the oven’s cabinet.
Recently, systems of polymers were developed, providing to the material, through special techniques, mechanical properties similar to those developed under the autoclave process.
This fact gives us the ability to manufacture products which incorporate high mechanical properties, without the use of expensive mechanical equipment, offering flexibility during the production process.

In this method a pre-treated piece of foam (epoxy, polyurethane, XPS, PVC etc.) is used, covered by the filament reinforcement which forms the final shape.
This method is often used for prototype and model production.

The foam which is enclosed by the material often remains, providing hardness and stiffness to the structure.