Silly Putty is a toy based on silicone polymers that have unusual physical properties. It bounces, but breaks when given a sharp blow and can also flow like a liquid. It contains a viscoelastic liquid silicone, a type of non-Newtonian fluid, which makes it act as a viscous liquid over a long time period but as an elastic solid over a short time period. It was originally created during research into potential rubber substitutes for use by the United States in World War II.