BOMBERHEAT® is a knit material with a velour-like reverse side created with a special raising processing. It doesn't use any functional yarns, but still feels really warm to wear. What's great about this material is that you don't have to worry about pilling on the raised surface. That means it leaves almost no lint on the clothing worn under it, and almost no fibers on the other clothes in the washing machine. Note: Our staff checked this by wearing it themselves.