GF, short for glass fiber, is an abbreviation for the English term "glass fiber". In the context of 3D printing, it refers to a composite filament, meaning a printing string, which is made up of a base plastic (for example, PETG or Nylon) with an admixture of short chopped glass fibers. The addition of these fibers to the material improves its mechanical properties. The resulting prints are stronger, stiffer, and have better dimensional stability, meaning they warp and deform less during cooling. Their thermal resistance also increases. Given that glass fibers are very hard, this material acts abrasively, meaning it wears down printer components. When printing with GF-type filaments, it is therefore necessary to use a nozzle made of a hardened material, such as hardened steel, to prevent its rapid wear.