Cut the polyester fleece to measure 45 inches square.
Thread the tapestry needle with the heavy thread. Sew a whip stitch around the perimeter of the fleece by inserting the needle every 1/2 inch, 1/4 inch from the edge of the fleece.
Insert the crochet hook into the first whip stitch and chain three. Stitch two double crochet stitches in each whip stitch around the perimeter of the fleece, stitching four double crochet stitches at the fleece corners.
Add or subtract double crochet stitches if the edging begins to pucker or wave up. Keep the edging flat, until the first row of edging has been completed around the fleece perimeter.
Chain three and add a scalloped border to the edging by crocheting five double-crochets in one stitch, skipping a stitch, one double crochet in the next stitch, skip a stitch. Repeat around the entire fleece, adding two extra double crochets to the corner scallops.