Tensile is a tan, globular material that sticks to itself in such a way that it forms globs or drops, like water with high surface tension. It will either float or sink in water, depending on the amount you drop on it and the height you drop it from. It is often used in Levels as the user element, and can make some interesting substances.
Tensile with the default settings isn't very stable. If the glob gets too big, the tensile force holding it together crushes the particles in the center, causing them to vibrate or even get thrown out of the blob. Tensile can be used to create nearly perfect spheres of Rigid. Chunks of the material RT stick together almost like magnets, and will begin to rotate slowly, known as the Tensile-Rigid reaction.