I primarily use 108" backs. I generally get them from Backsidequilters.com but you can find them at many sites; e.g., Keepsake, Hancock, etc. I found that most of the backing this size comes from Pakistan or China. Cottons from Pakistan, to me, warp much more than from other places. I've found this to be true on bed linens as well. I usually order 1/2 yard more than I need, wash it, then rip, instead of cut, at the raw edges so I'll get the true grain. Once I've done that I measure how much I need for the particular quilt and rip to get a piece with that measurement. It makes it much easier when you're putting your quilt sandwich together. If I don't have a use for the rest, I put it aside and donate it to a group that makes quilts for homeless children. They really appreciate the long strips they can get from my leftovers.