Fiberglass, and it is not easy to repair. I tried everything from a fiberglass repair kit, to super epoxy glue and they all broke within the same year. What i do now is use a thin sheet of stainless steel or aluminum and trim it to the size you need, drill holes and rivet it to the back of the hood. And if it is broken on a sharp corner, then i'll drill holes and just use alot of Zip ties because of the goofy angles. These DO hold. I've realized I would rather have a hood that STAYS together, than one that looks perfect.
Yes, the rivets may not be pretty to look at, but it's either that or shell out $450 for a new hood and $150 for a full sticker kit!
If anyone has tried something that also works well, I'd love to know.