The process of manufacturing fiberglass is called pultrusion. The manufacturing process for glass fibers suitable for reinforcement uses large furnaces to gradually melt the silica sand, limestone, kaolin clay, fluorspar, colemanite, dolomite and other minerals until a liquid forms. It is then extruded through bushings, which are bundles of very small orifices (typically 5–25 micrometres in diameter for E-Glass, 9 micrometres for S-Glass).

These filaments are then sized (coated) with a chemical solution. The individual filaments are now bundled in large numbers to provide a roving. These rovings are then either used directly in a composite application such as pultrusion, filament winding (pipe), gun roving (where an automated gun chops the glass into short lengths and drops it into a jet of resin, projected onto the surface of a mold), or in an intermediary step, to manufacture fabrics such as chopped strand mat (CSM), woven fabrics, knit fabrics or uni-directional fabrics.

Chopped Strand Mat (CSM) is made up of chopped strands of glass fibre laid randomly and held together with a binder or stitching. Chopped Strand Mat is designed to cover a wide range of layup techniques. It easily conforms to moulds and has fast wet out properties. Chopped Stand Mat can be chemically or mechanically bound. Chemical binders include Emulsion and Powder. Both chemical binders are highly soluble and work well with most resin systems. Emulsion is suitable for use with polyester while Powder binder is more suited to Epoxy resins.