Suction cups work by creating a vacuum between two surfaces. Made from flexible rubber or plastic, suction cups are non-penetrating and do not normally leave a residue, so they are useful for hanging lightweight items on glass, metal or other smooth and non-porous surfaces without causing damage. But some factors can make suctions cups work less effectively. To keep suction cups sticking, there are several things you should do.
Remove the suction cups from the surface. Place them in a sink filled with warm soapy water.
Dip a cloth in the soapy water. As the suction cups soak, clean the surface the suction cups had been attached to, removing any trace of dirt or oil. A dirty surface prevents the suction cup from making the necessary airtight seal. Rinse the soapy water off of the surface and then dry it with a lint-free towel.
Wash the suction cups with the cloth and rinse in warm water. Dry the cups with the lint-free towel.
Place the suction cups against the surface, one at a time, pressing down in the centre of the cup. As you press down, twist the cup just 1/8 of an inch to help push out all the air from beneath the suction cup and form the tightest seal.
Keep the cups and the surface they are attached to clean. How dusty or grimy the area gets will determine how often you should do suction cup maintenance. In general, check the suction cups once a week for sticking power.
Suction cups that have developed holes or tears, and suction cups that have been warped by heat, should be replaced. Cleaning damaged suction cups will do little to restore grip.
Direct heat, even from sunlight, can soften plastic or rubber, creating a break in the seal. The same thing may occur if the suction cup is exposed to freezing temperatures. Be aware of this when using suction cups on or near windows, or outdoors.