A hydrocolloid bandage is a flexible bandage made of water-absorbing material attached to a plastic film. The bandage adheres to the open wound with the absorbent film facing down. Hydrocolloids were originally designed for ulcers, but they are becoming more and more popular in acne, especially in Asia.
The tough outer plastic film is usually polyurethane, which can hold everything in place and prevent the evaporation of water and dry the wound, so the wound heals faster and the new skin formed is soft rather than tight and stiff. It also protects the wound from rubbing and scratching.
Water-absorbing materials are usually made of carboxymethyl cellulose, gelatin and/or pectin, and they have many water-binding groups in their chemical structure. This sucks fluid out of the wound. When the liquid enters the bandage, it will change from transparent to white and swell, which means you will get very satisfactory white spots