Ingredients in Fiberglass Resin

by Nicole Whitney
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Fiberglass resin is used to repair the bodies of cars and boats. Completed, dry fiberglass resin is made of fiberglass cloth bonded to the car or boat with resin and a catalyst, to make the resin harden. Each of these parts is comprised of different materials and chemicals, and when they come together, they create a light, hard material suitable for vehicles and even simple craft projects.


Fiberglass is made of exactly what it sounds like: glass fibers. Glass is made into extremely thin strands. These are then woven together to make fiberglass cloth or pressed in a random pattern to make other types of fiberglass mats. Fiberglass is considered an irritant because the little bits and microscopic pieces of glass threads can get into the skin or lungs, cutting and irritating them. It is essential to use protective gear when working with fiberglass. Fiberglass is still glass, but it is light and flexible when mixed with a resin. When the resin cures, the fiberglass inside gives it strength.

Polyester Resin

Resins come in many forms, and one of those is polyester. This is a different type of polyester than the one clothing is made from. Polyester resin is a polymer, which means the material's molecules are complex and often formed from the evaporation of water from the other chemicals in it. These chemicals are dicarboxylic acids and difunctional alcohols in polyester. Polyester resin is also unsaturated, which means it has an additional chemical in it that was not used in the reaction between the dicorboxylic acid and the difunctional alcohol. The catalyst to make these chemicals harden from a viscous liquid resin into a solid form are chemicals called reactive monomers, most often styrene. Reactive monomers are simply low-weight molecules that react with other chemicals to make polymers.

Epoxy Resin

Epoxy resins can be made with many different materials. The word "epoxy" comes from "epoxide," a chemical made of oxygen molecules combined with other molecules. The oxygen is added to molecules, often carbon, that are already bonded, creating a ring or chain of molecules. Epoxy resins tend to cure longer but stronger than polyester resins. The catalyst for epoxy resins is a hardener, often made from anhydride or amine chemicals. The amount of hardener changes the cure times and strength of the completed resin.

Other Resins

There are other resin types available for industrial use. Polyurethane is a familiar type of paint for many people, but it can also be used in resin. It is a polymer that engineers can use to create almost any desired affect. Vinyl ester resin is intended as an improvement to epoxy, creating a faster cure time and better workability. An epoxy is made with acrylic alcohol and dissolved in styrene to create the vinyl ester resin, and organic peroxides are used as a catalyst. Because these and other resins are used only in industry, the average person will encounter polyester resins as the most common fiberglass resins.

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