Fiberglass cloth along with resin (the hardener) is the shell on your traditional board or your Surftech. In both instances fiberglass is used along with as the structural strengthener of that shell. On a polyurethane shortboard, the accepted choice of cloth “weight” is a 4 and 6 ounce combo on the deck with a 4 ounce bottom. Longboards are heavier; usually with 4/6 ounce decks and 6 ounce bottoms.
There are two widely used types of fiberglass for the traditional polyurethane surfboard. “E” cloth is the most commonly used of the two. “S” glass is stronger but more expensive. You can use a combination of the two if you choose, but this is a custom touch and you must request it.
Check out surftech.com, salomonscore.com and avisosurf.com for a closer look at what goes into the “shell” of their alternative designs.