Gelatin is a protein extracted from animal collagen through partial hydrolysis. It is insoluble in cold water but soluble in hot water, where it forms a jelly on cooling. Gelatin is used to make hard and soft capsules, as well as suppositories, pastes and pastilles. It is also used as an absorbable sponge to control bleeding. Gelatin's properties are determined by its bloom strength, which measures its ability to form a gel.