Corricles are oval in shape, and look like half a walnut shell. They are made with a framework of split willow branches, twisted together and tied with willow bark. Originally the outer layer was an animal skin from a horse or bullock. These skins were covered with a thin layer of tar to make them keep the water out. Today coracles are made with calico or canvas covered in tar, or simply fibreglass. The Asian coracle is made differently. It uses bamboo and the water is kept out with a layer of resin and coconut oil. The coracle does not have a keel. The flat bottom allows the weight of the boat and its load to be spread evenly. This means it does not need much water to float – as little as a few inches, making it ideal for use on rivers.