I am trying to figure out the best sacrificial material to use on the waterjet for a sheet of double mirrored stainless steel (.125''). Typically I only use foam as my backing material, and then only for very delicate work like glass and acrylic, so I'm wondering what people typically use to avoid splashback and edge frosting on polished metal. I've heard of rhinoboard and jetbrick, which are products designed for this purpose, but I'm not sure if they are worth the money, and if maybe I can get a similar result from something lying around the shop. Will ply warp too much?