Blu Tack is a reusable putty-like pressure-sensitive adhesive produced by Bostik, commonly used to attach lightweight objects (such as posters or sheets of paper) to walls, doors or other dry surfaces. Traditionally blue, it is also available in other colours. Generic versions of the product are also available from other manufacturers. The spelling now used is without the hyphen.
The composition of Blu Tack is a manufacturing secret but is described as a synthetic rubber compound without hazardous properties under normal conditions. It can be swallowed without harm and is noncarcinogenic. It is non-soluble and is denser than water. The material is not flammable, but emits carbon dioxide and carbon monoxide when exposed to fire or high temperatures.