WARM TIPS. This powerful shower suction shelf works best on non-porous, impervious, smooth surfaces such as glass, mirror, polished metal, stainless steel, plastic board, wall tile, grainy granite, etc. Please remind that don't stick to grout line and porous surfaces such as: wood, unfinished marble, porcelain, wallpaper, natural stones (such as Travertines), painted wall, etc.