Fiberglass

Fiberglass is the common name to glass fiber-reinforced composites, or GFRPs.

The glass fibers are the main source of the mechanical strength. They are held in place by a polymer matrix. The most common matrix is epoxy.

Glass is ordinarily very weak, but if it is drawn out into long fibers, then the Weibull statistical distribution of the surface flaws guarantees that, provided a sufficient aspect ratio, that they will be able to exhibit shear transfer through the matrix enough to overcome each the flaws in each fiber of a critical size.