The intrachain and interchain vibrations below 900 cm−1 of polydimethylsiloxane (PDMS) have been studied by slow neutron inelastic scattering. A composite motion observed at +25°C for the methyl groups corresponds to nearly free rotation about the threefold axis of symmetry together with a large‐amplitude rotation of the entire methyl group. At −123°C, rotation about the threefold axis evolves to a torsional oscillation. The large‐amplitude rotation evolves to the skeletal vibrations of a helical conformation. Vestiges of the cooperative skeletal vibrations of the conformation at −123°C persist into the 25°C spectrum. The results indicate the presence of interrupted helical conformations at 25°C, which result from thermal disordering of the low temperature helices. The effects of crosslinking, low molecular‐weight oils, and silica filler on the freedom of the methyl group motions and on skeletal vibrations have been determined. The effects of different crosslinking agents and different relative amounts of filler and oil on both the macroscopic physical properties and the observed molecular motions of PDMS can also be interpreted in terms of an interrupted helix.