The new Pirelli Mousse is a toroidal-shaped expanded-foam insert which replaces the traditional inner tube on off-road motorcycles. Technically the mousse is a butyl ring with a honeycomb structure, the cells of which are filled with gas so as to simulate the effect of an inner tube.
A Pirelli Mousse is a technologically advanced product, characterised by the presence of self-pressurising agents capable of creating a very large number of gas bubbles inside the mousse, making the product immune to punctures.

A Pirelli Mousse therefore has an evident advantage with respect to traditional inner tubes, given that in use it is immune to punctures and abrasions. It has been developed by Pirelli for riders who compete in every kind of competition, whether it be a race in the desert or a Cross championship trial. From the point of view of construction the Mousse is surrounded by a thin external membrane designed to make it easy to fit on different sized tyres.

The Pirelli Mousse is designed for use with Pirelli tyres on off-road surfaces. The NHS (Not for Highway Service) rating means that they are not recommended for road use. When new, they are equivalent to an inner tube inflated to 0.9 bar (equivalent to approximately 13 PSI). This pressure declines gradually along the life of the mousse, which must be replaced when it becomes too soft.