108" Roc-Lon cotton or I'll piece my backs in 3 sections (when I do big ones)... I also have 90" fabric which is great for the twin size or smaller, but I love 100% cotton! It's more hot here than cold, so this will depend on where you live, who's going to use it (child heavy usage, adults not so much)...

Good luck, can't wait to see how you finish your's up

:-Debbie