Hook and loop is one of the most popular fastening systems in the world today. Sometimes, it's referred to as a hook and pile or touch fastener. What is the difference between hook and loop tape? One side is called the hook and the other side is called the loop. Wondering which side is which? The rough side is called the hook. And the soft side is called the loop Hook and loop fasteners have two strips; the rough side has hundreds of tiny 'hooks' and the softer side has hundreds of tiny 'loops'. When you press the two strips together, the hook cling to the loops to make them stick. The more hooks and loops that are attached, the stronger the hook and loop fastener will be. When the two are pressed together the hooks catch in the loops and the two pieces fasten or bind temporarily. When separated, by pulling or peeling the two surfaces apart, the strips make a distinctive ripping sound. The hook side will always find loop to attach to because hook is covered on the entire front side and loop the entire back side.