I the FMQ class I took the teacher recommended cutting the batting in a curve shape before sewing it together. Said it would hold together better when it was quilted. If you cut straight it could end up in a spot that didn't get much quiting. She also recommended buying fusible tricot to use as an iron on to piece batting. You can get it in the interfacing section. The stuff they sell to fuse batting together is just a thin strip of fusible tricot. Much cheaper to cut your own strips.