I've backed with denim (heavy, makes the bow sluggish), light canvas (not quite as bad), and light shirtweight cotton (tough and doesn't slow the bow much). I'd recommend you go to my favorite...antelope rawhide. It's about as thick as butcher paper and bloody near as tough as kevlar!!! Bombproof when applied correctly.
Send me a p.m. and I'll hook you up with my supplier, he is also a regular advertiser in P.A.