Warm Tips: The suction cups are only stick on smooth, non-porous surfaces like metal, glass, tile, stainless steel and acrylic but not apply to uneven tiles, texture plate, unfinished marble, wallpaper, painted wall, etc. Incorrect installation will cause the vacuum loss of suction cups. If problems when firstly installation, please wash the suction cup, dry it with hair dryer and test it on the smooth glass surface. If suction holds, that means initial wall might not applicable for using suction cup, please change installation location Hassle-free Installation: Simply press down the suction cups with palm to squeeze the air out, they will stick to the wall firmly. You can finish the installation in 1 second, and put your items in the shelf immediately without waiting 24h. No screws, no nails, no glue needed.