Choose a plastilina clay if you need to work slowly and do not need your sculpture to harden. Plastilina clay is a nonhardening oil-based modeling clay. This type of clay uses wax instead of water, so it will not air-dry. There are different brands and levels of hardness to choose from when selecting a plastilina clay. This type of clay is typically sculpted into a sacrificial model that is used to make a mold for additional reproductions. Plastilina clay can also be heated and poured into a mold.
Multicolored plastilina clay is ideal for use in stop-motion clay animation. The clay is stiff enough to use alone with small figures, or armatures can be used for larger figures.
Choose polymer clay if you plan to make smaller models, and the final form will be the sculpture. Polymer clay is usually a lot more expensive per weight. It is soft at room temperature and is hardened by heating at a temperature between 265 and 275 degrees Fahrenheit.
Choose an air-dry clay for general purpose sculpting. Air-dry clay is water-based and will harden as it dries. To work with air-dry clay over several days, the clay will have to be kept moist and covered. Review the clay manufacturer's specifications for shrinkage. Typically, clay with less shrinkage will cost more than clays that tend to shrink and crack.
Choose WED clay if you are sculpting a large figure. WED clay, also known as EM-217, is a fine grained water-based clay originally developed by Disney Studios. It is extremely good for sculpting large figures since it is slow-drying and has a low shrinkage and cracking rate. WED clay can also be found for less than $1 per pound. Generally, you will only need to air-dry WED clay, but it can be fired if needed.