He wears it throughout the series when he isn't wearing that leather and PVC catsuit. Which - contrary to what he says on an interview, there were a number of those made for him, all of which were "more or less ruined during filming."
Question to ponder in XMen-3 - If Phoenix was SO DARNED POWERFUL how come she couldn't disintegrate the pants off Wolverine in the final confrontation? Does he have adamantium undies?