an air bag cover for use in a supplement inflatable restraint system includes an air bag cover skin made of a polymeric material . the cover skin includes a weakened tear seam region for guiding the tearing of the air bag cover skin in response to air bag inflation . the tear seam region is weakened by photodegradation , i . e ., selective exposure to ultraviolet light which breaks polymer bonds within the polymeric material of the tear seam region . photodegradation reduces the tensile strength and / or the percent elongation of the tear seam region compared to the rest of the air bag cover skin .