A few years ago when i got my first tube of Hysol I did a little test of it in compariosn to Devcon 30 minute epoxy. Using each glue I stuck a piece of 1/4" balsa end on to a piece of epoxy glass board, and left them for a couple of days. I then pushed the top end of the balsa stick to see how much effort it would take to either break the wood or the glue joint. The devcon joint snapped cleanly away from the board with just a little force taking a perfect imprint of it and leaving no devcon at all on the board. It had barely stuck at all The Hysol required a lot more effort and tore very thin bits of the board surface with it. Therefore in my experience Hysol sticks to fibreglass much better than normal epoxy, it isn't simply epoxy with thickeners.