Akzo has developed a fabric based on Enka nylon filament for use in air bags. The fabric is constructed in a 2x2 basket weave for high permeability and controlled air release. A jacquard loom is used to weave the fabric. The fabrics are not coated. Coated fabrics used in air bags have caused burns because of the high frictional force generated on release. Ultimately, some combination of gas-permeable and gas-impermeable fabrics will be used in air bags to eliminate any adverse effects caused by escaping gas. Because fabric density critically influences permeability, both properties must be quantified to define specifications. heat treatments can be used to increase permeability as needed. The properties of polyester air bags are compared with those of nylon air bags.