Aluminum, 3mm sheet,
Its bolted to the bumper with captive nuts. I used 2 "L" shaped pieces, riveted to form a box, as a support under the radiator lower mounts. The tray is bolted to these to provide extra support. The idea behind the "box" support was to allow it to deform if there was any contact with speed bumps or the like, rather than damage the rad ot its mount. So far its all good.