A textile used on the unseen or "wrong" side of fabrics to make them more rigid. They come in a variety of weights and stiffnesses to suit different purposes. Generally, the heavier weight a fabric is, the heavier weight an interfacing it will use. Most modern interfacings have heat-activated adhesive on one side. They are affixed to a garment piece using heat and moderate pressure, from a hand iron for example. This type of interfacing is known as "fusible" interfacing. Non-fusible interfacings do not have adhesive and must be sewn by hand or machine.