And here's the other side, showing a CSM mat stiched to the bi-ax. This should produce a thicker and hence stiffer sheet than pure bi-ax of the same weight. It's a bit too heavy to lay over carved foam however. I'm using 300 gm. bi-ax, backed up with a layer of 400 gm. in impact areas where the good tear resistance of Bi-ax is more important than surface stiffness.

But people making epoxy sections, using moulds, which lack the stiffening of internal foam filling will probably find this a very useful way of getting enough surface stiffness and avoiding internal ribbing or unwanted section changes.

This came from Matrix Mouldings Ltd. in Days Road Bristol, suppliers of GRP products to everyone from roofers to performance boats. I'm not one of their larger customers...