E-glass is your more common, everyday fiberglass cloth. It's formulation was originally developed as an electical wiring insulation. The 'E' stands for electrical.
The composition of the glass fibers in S-glass were developed specifically as a structural material. It is 30% stronger and 15% stiffer than E-glass, according to
Aircraft Spruce and Specialty.
The homebuilt aircraft community would be a good source of information for the use of fiberglass/foam composites in structural applications. I haven't got a hold of a copy yet, but I hear Burt Rutan's manual; "Moldless Composite Sandwich Aircraft Construction", is the accepted bible of the technique.
Nice progress so far!
