heat - expandable molded synthetic resin seal and baffle components adapted for use in automobile body cavities or the like are provided which are designed to preferentially expand upon heating in desired directions and to a desired degree , in order to properly seal irregular or special cavity shapes . the molded components of the invention have selected body surface portions thereof uv crosslinked to a depth of up to about 0 . 5 mm , while other portions of the molded body are not crosslinked ; upon heating , the crosslinked portions expand at a slower rate and to a lesser extent than non - crosslinked body portions . the preferred synthetic resin includes a grafted anhydride polymer , a terminal epoxide polymer additive , a blowing agent , a uv photoinitiator and a uv crosslinkable resin system .