E-glass

One category of Fiberglass, the other being S-glass

E-glass, which stands for Electrical, is the common, all-purpose type. When someone justs says, “fiberglass,” they almost invariably means E-glass. S-glass, which stands for high-Strength, is stronger, stiffer and more expensive. What is commonly called S-glass nowadays is actually S2-glass. The original S-glass, sometimes called military S-glass because it was developed for military applications, is somewhat stronger than S2 glass but it is extremely expensive, due to stringent testing and certification requirements of the military. There is no chemical difference between S and S2. The stringent mil-spec testing will pass only the highest quality material, while the commercial S2 material may be slightly less strong and still pass its test. S2 glass was developed in the 1960s by Owens-Corning to bridge the gap between E-glass and mil-spec S-glass. Compared to E-glass, S-glass provides about 40% higher tensile and flexural strengths, about 10 to 20% higher compressive strength and flexural modulus, and greater abrasion resistance.