It depends. Allot of people use WED clay, however you have to make sure it doesn't dry out. It's a rather cheap clay you can get online. Personally I highly recommend Monster Clay, as it's oil based (meaning it gets softer when you apply heat, and harder if you apply cold) and it can't "dry out" so you have unlimited work time. It's also easy to reuse. Drawback being a 5lb tub of it is about 40$ shipped.