:Since Boeing builds using mostly Epoxy resins(some cyanates these days) you'll be wanting to know just which sizing is on the glass you bought. If you are planning on using epoxy, then chances are that you are fine with it. On the other hand, if you want to use vinylesters,or polys on the epoxy compatable sized glass, you will not get optimum results. They usually have lot/batch tracabilty to the fabrics.Sometimes a small roll tag is inside the paper core. Too bad you did not get that documentation. Call them back!

Being E or S is not going to impact your boatbuilding much I suspect. A simple, relative test that will work to see which modulus fiber you have is to make three identical glass panels using known S and E and your new batch-say 6 plies and 2" X 9". Then cantalever them off a table top (clamp them down)and hang a known weight from the overhanging panel and simply measure deflection and compare. You don't need to break them in a fancy machine to tell what you have on this one. But that would work too. Hope this helps. RL