Classical rotational inertia of solid helium 4
  The observation of reduced rotational inertia in a cell containing solid helium 4 has been interpreted as evidence for superfluidity of the solid. An alternative explanation is slippage of the solid at the container wall due to grain boundary premelting between the solid and dense adsorbed layers at the container wall. We calculate the range of film thickness and the viscous drag, and find that the slippage can account for the observations. 
J.G. Dash, J.S. Wettlaufer