Kinetic Sand

Kinetic Sand is made of 98% fine-grained sand and 2% polydimethylsiloxane (a type of silicone oil). It is a granular material that exhibits an unusual mix of solid and liquid properties depending on what you do to it. Try sculpting a shape out of the sand, or cut it with a knife: it should behave just like wet sand and harden on impact to become mouldable or sliceable. However, when disturbed or left to its own devices, it will slowly flow and lose its shape. This material was originally designed for sculpting, it sticks to itself but not most other surfaces, and it does not dry out.