After everything is inspected, it goes into the glass beading cabinet. This is the plenum box, and as we said, it's made of fiberglass. The glass beading leaves it looking white. If you do it yourself, take care to use low pressure. Notice that the factory numbers painted on the box (circled) are still there. Classic Auto Air masks off any factory markings before bead blasting to insure they aren't obliterated and lost forever.