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Fiberglass Mat FAQs

What is fiberglass mat (aka chopped strand fiberglass)?

Fiberglass mat, also called chopped strand fiberglass or chopped strand mat is a non-woven material composed of short glass fiber strands. Although fiberglass mat is not very strong by itself, it is an economical way to reinforce fiberglass cloth or fiberglass woven roving in varied applications.

Available in various widths and sizes, Fiberglass mat is also ideal for building thickness and stiffness into laminate repairs, build-ups, and mold-related projects.

How is chopped strand mat created?

Producing chopped strand fiberglass is a multi-step process. First, a machine cuts continuous strand fiberglass roving into short lengths, each 1.5 to 3 inches long. Next, the cut fibers are randomly scattered over a moving belt, creating a loosely structured random fiber sheet.

To provide structure, a lightweight binder added to the mostly formed fiberglass sheet. Next, the mat is trimmed and formed into a roll. You can also purchase chopped strand mat in tape form.

What is the difference between fiberglass mat and cloth?

Fiberglass mat is a randomly oriented sheet of short glass fibers. Although it is not very strong, it is isotropic, meaning it displays equal strength in all directions. It is ideal for making parts and creating molded objects and is also used to enhance fiberglass cloth thickness.

Fiberglass cloth is a woven material with yarns oriented at 90-degree angles. This creates a fabric that is anisotropic, or strong in just two directions. Fiberglass cloth is available in a simple over/under plain weave pattern. In addition, varied types of satin weaves incorporate a filling yarn among the warp yarns. The satin-weave fiberglass cloth is stronger than the plain-woven cloth, and also conforms better to curved surfaces.

How do you choose between fiberglass cloth or mat?

Fiberglass cloth and fiberglass mat are considerably different materials. Fiberglass cloth is a class of woven fabric that is available in several different types of weaves. If you want to create a lightweight (but strong) laminate, fiberglass cloth is your best bet.

Fiberglass mat, features randomly oriented fibers without defined patterns. This property makes it the best option for creating complex shapes and tight corners when used with a mold. However, the mat is not very strong, so choose woven cloth or blend the two fiberglass products.

Chopped strand mat provides extra thickness when fabrication parameters require it, and helps to strengthen the bond between layers. In a gelcoat laminate, the mat is commonly used to prevent print-through, which occurs when the fiberglass texture is visible through the resin.

How do you use chopped strand fiberglass mat?

With chopped strand fiberglass mats random fiber orientation, it is easy to process this reinforcing material using a hand lay-up method. First, place sheets of material on a mold. Next, thoroughly brush the sheets with resin.

Note that polyester and vinyl resin effectively dissolves the binder that holds the sheets together. When the binder is gone, the chopped strand mat will easily conform to most desired configurations when saturated with the resin.

After the resin finishes curing, remove the resin-hardened product from the mold.

Do you use epoxy resin or polyester resin with fiberglass mat?

Polyester resin and vinyl ester resin are good fiberglass mat wetting agents. Both resins contain styrene, a substance that breaks down the mats binder during the lay-up process, allowing for good resin saturation. Epoxy resin does not contain styrene, so it is less suitable. Wetting out chopping strand with epoxy results in a stiffer material, and should be limited to flat or slightly curved surfaces.

Due to the nature of CSM, multiple coats may be required. Note that some types of fiberglass mat do not contain binder, such stitched mats work vastly better with epoxy resin, and may be used both above and below the waterline.