Glass reinforced plastics, sometimes referred to as fibreglass reinforced plastics, make use of a relatively new type of composite material to greatly enhance the physical properties of plastics. Glass reinforced plastics can be found anywhere from surfboards to fighter jets and now as 3D printing filaments
Fibreglass is composed of extremely fine glass fibres that have been woven into a flexible sheet which can be reacted with a plastic resin, often in the presence of a catalyst. The result is a strong, lightweight plastic that also demonstrates great thermal insulation.
An important note when 3D printing with glass reinforced filaments is that they can be quite abrasive and wear down your hot end. A hardened steel hot end is usually recommended.
Glass reinforced filaments are ideal for products that require high strength and stiffness whilst being exposed to high temperatures.