S-GLASS stands for structural fiberglass. It is 30% stronger than regular fiberglass and about 15% stiffer. It also costs more than twice as much! But when you are buying a high end product it is important to pay a little extra for the things that will make it last. Our S-Glass skimboards have multiple layers of S-Glass on each side. This makes the board a little stronger than an eglass board of the same weight and a little bit stiffer too.