Soaps when used in hard water form insoluble precipitates which separate as scum in water and are useless as cleansing agent. In fact these are hindrance to good washing, because the precipitate adheres onto the fibre of the cloth as gummy mass. On the other hand, synthetic detergents can be used both in soft and hard water as they give foam even in hard water. Some of the detergents give foam even in ice cold water.