Silly Putty is a toy based on silicone polymers that have unusual physical properties. It bounces, but it breaks when given a sharp blow, and it 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.

The name Silly Putty is a trademark of Crayola LLC; the company’s factory is based in Easton, Pennsylvania, USA.  Other names are used to market similar substances from other manufacturers.