Fiberglass is a material with an average density of 1.7 kg/m3 and the most commonly used fiberglass types are E-glass, S-glass, and R-glass. The differences in densities has to do with the different compositions of each type (E=ethylene glycol; S=silica; R=rayon). It can be used for insulation, reinforcement of plastics and other materials, and in construction.