When I needed to "bulk out" in costume... as a spontaneous transformation, I used inflatable life-vests. I made the understructure, then a pocket of two-way spandex. I worked the life vest panels down the arms, across the back shoulders. Then added my outer detail in overlapping panels, so when it expands, it still covers. Start to twitch, crouch down, pull the cords and snap up dramatically as it inflates! :cool