The natural sponges we use in our baths are actually animal skeletons. Bath sponges consist of a highly porous network of fibres made from a collagen protein called spongin. The skeletons are obtained by cutting the growing sponges and soaking the cut portions in water until the flesh rots away. The exposed network of spongin fibres is cleaned and bleached. In recent years New Zealand scientists have investigated the possibility of farming a native species of bath sponge, Spongia manipulatus, for commercial production. Sea sponges have been over-harvested from the major sponge-gathering areas around the Mediterranean, Caribbean and Florida coasts, but demand remains high. Pictured here are two New Zealand bath sponge skeletons, bleached (right) and unbleached.