I have used a paperclay and a Japanese clay made with "wood powder". Both are air-dry clay and super lightweight. After pressing the clay into the mould, smooth the surface, then you can gently bend the mould and the item will pop out, then set it aside to air dry. That way you can make multiple images and not have to wait for them to dry in the mould. I use these images on my greeting cards, and my art-box projects. The air-dry clay has worked very well for these projects.