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 matt is not very strong by itself. it is an economical way to reinforce fiberglass cloth or fiber glass woven roving in varied applications. Available in various widths and sizes. Fiberglass mat is a so idea for building thickness and stiffness into laminate repairs, build-ups,and mold-related projects.