Polymer Clay- needs to be baked. It is waterproof and hard. Made of PVC plastic.
Modeling Clay- the all time favorite of kids. Non-drying and reusable.
Ceramic Clay- no need to fire. Just air dry. It can be painted when dry and varnished to become water resistant. To achieve porcelain, it must be fired at 1000 degree Celsius.
Air Hardened Clay- no need to bake. Just air dry. It is fortified with fiber to make them more resistant to cracking. After dry, it can be painted and varnished to become water resistant. Special techniques for Focus Air Hardened clay. (http://www.focusstationery.com/clay2.html)