A vehicle seat assembly includes an air bag arrangement having an inflatable air bag, and a cover material overlaying the air bag arrangement. The cover material has first and second sections that define a seam through with the air bag is deployable. A retainer is connected to the first and second sections of the cover material, and the retainer has a frangible portion. Upon inflation of the air bag, the retainer is configured to separate proximate the frangible portion to allow the air bag to deploy between the first and second sections of the cover material.