First you need decide what kind of fiberglass you want to use. Do you need to build up thickness fast? Are you concerned about strength? Do you have tight corners you are working with? Let us help you decide if fiberglass cloth is right for your project or if you are needing chopped strand mat.
Fiberglass Cloth is a woven fabric. Plain, 4 harness satin and 8 harness satin are the weave styles we carry. The 5.6, 6, 7.5 and 10 ounce plain weave fabrics are the most commonly used. In this simple plain weave pattern, warp and fill yarns are interlaced over and under each other in alternating fashion. The plain weave is the easiest to handle since it does not unravel as much as the other weaves when cut.
In the four-harness satin weave pattern there is a three by one interfacing where a filling yarn floats over three warp yarns and under one.
The eight harness satin is similar to the four harness satin except that one filling yarn floats over seven warp yarns and under one.
The satin weaves are slightly stronger and more pliable than the plain weave and are easier to conform to curved surfaces. They are more difficult to handle than the plain weave, though.
Use fiberglass cloth when you are looking to create a strong, light weight product.
Chopped Strand Mat (also known as fiberglass mat) has short strands of fibers held together with a resin binder. The fibers are randomly oriented. Mat is only compatible with polyester and vinyl ester resin. When resin is added to the mat, the binder dissolves and the fibers can be moved around. It is easier to conform mat to tight curves and corners than it is with weaved fabric.
The reason chopped strand mat is not compatible with epoxy resin is because the binder holding the fibers together needs styrene to properly dissolve. Polyester and vinyl ester resins have styrene in them. (There are some places that sell chopped strand mat that is compatible with epoxy but it is hard to come by and much more expensive).
Chopped Strand Mat is the least expensive fiberglass and is often used in mold construction or projects where thickness is needed. Mat is often used as the first layer (before the gelcoat) in a laminate to prevent print through. Print through is when the fabric weave texture shows through the resin.
Chopped Strand mat does not have much strength. If you need strength you should choose a woven cloth or you could mix the two. Mat can be used between layers of woven fabric to help build thickness quickly and aid in all layers bonding well together