Hook is Made of 304 Stainless Steel, Knob Cup is Made of ABS Plastic and the sticky rubber pad is washable and reusable.
If it doesn't work, please make sure suction cups are not over group btween tiles, and uninstall the suction cups into three parts, wash and dry the black rubber before installation.
then press the black rubber pad to make sure that every corner of it is tied to the wall surface,