Hi Stephan, the Tree man was made from Aves Apoxie sculpt which won't crack and like Milliput and Greenstuff drys by chemical reaction, the disadvantage to this clay is it's speedy drying time but it's really tough.The reason the tin foil was used is to save money on clay.The Ogre is made from Super Sculpey medium which can crack if applied in a thickness of over half an inch. Still finding my way with armatures as I don't want to apply too much tin foil then not be able to sculpt to the required depth.Although on my Great unclean one sculpt I used the Dremel to get some depth back in a couple of areas.The advantage to Super Sculpey is it stays wet until baked so you can take your time which is perfect for more complex projects like the Ogre where i'm not so confident.However Sculpey is brittle and can break easily once hardened.