The matrix acts to bond and encapsulate the fibers, enabling the transfer of loads from fiber to fiber.
It also protects the fibers from degradation due to environmental effects, including: moisture, UV radiation, chemical attack, abrasion and impacts.
Polyester Unsaturated polyester resins achieve cross-linking through a multiphase reaction.
They are inexpensive and provide fairly good environmental resistance.
Polyesters have lower strength and exhibit higher shrinkage than epoxied during cure.
They generally contain between 30-50% styrene in the formula, producing considerable emissions.
Vinyl Ester They achieve cross-linking through a multiphase reaction, and yet offer better environmental resistance, strength and fiber adhesion than polyester resins.
They exhibit less shrinkage than polyester. Their cost is also in between polyester and epoxy.
Epoxy The workhorse of the advanced composites industry, epoxy resins offer better physical and adhesion properties than polyester or vinyl ester.
Epoxies cure by cross-linking reactive polymers at both room and elevated temperatures.
They provide good environmental resistance.
Phenolic They are fairly brittle, with poor adhesive characteristics, but have excellent static-dissipative properties and exhibit good chemical resistance.
Stable at slightly higher temperatures than epoxies, phenolics offer good flame resistance and low smoke toxicity.
Polyimide Polyimides exist in both thermoplastic and thermoset formulations.
They require a high temperature cure and can be difficult to process.
They provide good flame resistance and low smoke-toxicity, but are fairly expensive.

Thermoset resin & Thermoplastic resin

Thermoset Resin Thermoset resins are the most widely used matrix material in composite materials. They achieve cross-linking through a multiphase reaction.
There is three 3tages, which describes its status regarding chemical reaction and cure.
1. A-stage: It is the first stage, characterized by low viscosity and the ability to be diluted with solvents.
2. B-stage: It is the stage, where the resin is somewhat viscous and tacky, but not flowing. When heat is later applied during the cure process, the resin viscosity will drop and flow and the chemical reaction will proceed.
3. C-stage: This is the final reaction stage in which the resin has cross-linked to the point where it is insoluble and infusible.
Thermoplastic Resin Thermoplastic matrix materials undergo a physical change from a solid to a liquid when heated, and then re-solidify upon cooling.