Cotton holds the fabric securely to the batting and helps the quilt hand flat. Cotton "breathes". It is cool in the summer and warm in the winter. This product is made using bleached white cotton. The special blend fiber makes this batting feel soft to the touch and allows the needle to glide more smoothyly through the batting, preventing "pops" on the underside of the quilt. This fiber, in the amount present, helps prevent creases from forming when the quilt is folded. Machine 60/40 blend has a thin scrim to prevent stretching and to help the batting maintain its integrity on a larger frame. The scrim also prevents tearing and migration. Long Arm, Short Arm, & Domestic Machine 60% Cotton - To hold fabric securely to the batting and allow the quilt to hang flat. 40% Special Blend Polyester - Softer to the touch, allows needle to glide through the batting, helps prevent "pops" under the quilt, helps prevent creasing when the quilt is folded.