Wonder Under is a fusible designed to stick one fabric to another, adding no weight or strength .....fusible interfacing comes in many different weights and is designed to give strength to finished item, like collars, buttonhole areas, etc......am guessing the fusible fleece is designed for quilters, to make the quilting process easier - giving the loft and some strength to a finished item while holding the fabric and batting in place (no slips or puckers).