A motion describing the dynamics of a polymer in a highly entangled state, such as a network. Regarding the entangled state as a set of chains between crosslinks it is possible to regard the chain as being in a ‘tube’, with the tube being formed by topological constraints. The chain is longer than the tube so that the ‘slack’ of the chain moves through the tube, which causes the tube itself to change with time. This motion was called reptation (from the Latin reptare, to creep), by the French physicist P. G. de Gennes, who postulated it in 1971. Many experiments indicate that reptation dominates the dynamics of polymer chains when they are entangled.