The ready-made material is an epoxy-glass laminate called G-10. It
comes in sheets bars rods and tubes and is available fgrom mcmaster-carr
(search for garolite g-10) and from other plastics distrubutors.

Alternatively, you can make your own with leftover glass and epoxy.

Robert or Karen Swarts wrote:

A few days ago some one was discussing fiberglass backing material for
anchoring fittings. Can some one tell me if it has a specific brand name and
where I can get it?

Thanks,

BS