0.75 oz Fiberglass Mat - 38" x 3 yd

Chopped strand mat consists of randomly oriented, chopped strands of glass fibers, held together by a polyester binder.
When polyester resin is applied to chopped mat fabric, the binder dissolves - allowing the resin to soak into the fibers. This results in a strong, fiber-reinforced structure.
When the binder dissolves, the fibers also have the ability to shift, somewhat, within the mat/resin matrix. This can make it easier for mat to conform to tighter curves and corners than woven fabrics.
Mat fabric is compatible with unsaturated ortho-polyester, iso-polyester, vinyl ester, and a variety of other solvent-containing resins.

The use of epoxy resins with chopped strand mat, however, is not recommended since the epoxy resin cannot dissolve the polyester binder.
This prevents the epoxy resin from saturating the glass strands. Instead, the epoxy resin merely coats the fibers, leaving microscopic air pockets — resulting in a weaker finished structure.
When using epoxy resins, Fiberlay recommends using only woven fiberglass cloth or roving fabrics — which require no binders since the weave itself holds them together.

Being relatively inexpensive, mat is commonly used for building thickness in diverse fiberglass structures, such as mold construction, panels, plywood decking, fiberglass furniture, and between layers of fabric when molding storage tanks and boats.
Chopped strand mat is also used as a backing for gelcoat, as it has less pattern transfer than most woven fabrics — so is less likely to show through the gelcoat.

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When comparing various weights of fiberglass fabrics remember:
Fiberglass woven cloth and roving is measured in ounces per square yard, while fiberglass mat is measured in ounces per square foot.
So a square yard of 1 oz mat is the same weight as a square yard of 9 oz cloth.


Heavy on the technical side...Some Application Tips

When building fiberglass structures using polyester resins, and where impact resistance is important, alternating layers of chopped strand mat and woven fiberglass cloth or roving will result in a stronger structure than using layers of woven cloth alone - which can delaminate under impact.
In this situation, the layers of mat bond to the woven cloth fabric better than the cloth does to itself.
As above, when using epoxy resins, only woven fabrics should be used for the strongest results.

When covering wooden structures - such as a wooden boat - with a layer of fiberglass cloth using polyester resins, you should not apply the woven cloth directly to the wood. Always start with a layer of lightweighjt mat - which acts as a binder between the wood and the woven fabric.
When cloth fabric is applied directly to wood, it can readily delaminate, whereas if mat is applied first, often the wood will fail before the mat can be peeled off.
Again, when using epoxy resins, cloth can be applied directly to the wood and result in a strong, permanent, bond.