The inner skeleton can actually be made from a variety of cheap materials. The engineers folded up pieces of soft silicone rubber, for instance, as well as sheets of clear polyester. They even conducted successful tests with water-soluble materials, which could be used to make medical or environmental robots capable of dissolving in-situ when finished with their work. In a robot where total squishiness is not of the utmost concern, metal coils could provide extra strength, or the skeleton could be made of electronic boards to allow for screens or color changes. Depending on the material, the researchers note, any manner of fabrication technique—3D printing, machining, casting, forming, and even manual folding—might be used.