Biaxial Fiberglass

1708, 1808 and 1208 stitched biaxial, by the yard or the roll

Biaxial fabric is stitched, not woven. The fibres run straight at plus and minus 45 degrees instead of crimping over and under each other, so they carry load without first having to pull straight. That is why a transom or a stringer built in 1708 is stiffer than the same weight of woven roving.

Reading the number

The first two digits are the weight of the biaxial glass in ounces per square yard. The last two are the chopped strand mat stitched to the back. So 1708 is 17 oz of biaxial with 0.8 oz of mat, and 1208 is 12 oz with the same backer. The mat is there to give polyester resin something to key into against a smooth old hull, and to build a resin-rich layer that helps the laminate conform.

The mat backer decides your resin

That stitched mat is bound with a styrene soluble binder, which polyester and vinyl ester dissolve and epoxy does not. 1708 still works with epoxy and plenty of people build with it that way. The mat simply stays intact rather than breaking down, so it acts as a ply of its own rather than merging into the laminate, and it drinks more resin. If you want biaxial with no mat at all for an epoxy layup, DB170 is the same 17 oz biaxial without the backer.

Which weight

1708 is the standard for transoms, stringers and structural hull repair, and it is what most repair manuals call out. 1808 is a step heavier where you want fewer plies. 1208 is lighter and more conformable for tighter radii and smaller repairs. 1708 tape saves cutting strips when you are taping a stringer or a chine.

Planning the schedule

The layup calculator builds a full ply schedule and returns cured thickness and the resin each ply takes.