Non-toxic, skin safe, and lead-free, Worbla's Deco-Art comes in white pellets that when heated (to 65C/150F) turn clear. You can treat these clear pellets like a plastic putty and sculpting material, either shaping them by hand or with tools or applying it directly to the surface you wish to build up. Once cool or 'set' the plastic turns opaque white.
It's an excellent option for sculpting things like skulls, filling in gaps in Worbla armor, making multiple copies of something without resin casting, building up dimension quickly, and adding counterweight to things like pommels on swords.