i piece batting together all the time. i don't worry about what the fiber content is...as long as all of the peices i am putting together are the same. i just butt them together and zigzag with a large stitch. poly, cotton, wool...if it's batting and i need it i put it together and use it. i think there is some new product on the market that is like a batting tape you can use to attach peices but i do not know what it is like or it's properties. since i just sew my batting pieces together i see no reason to waste money on a product like that but that's just me...