Indentation tests at indentation depths from 200 nm up to 100 mu m were performed on polydimethylsiloxane ( PDMS). The universal hardnesses in the elastomer were determined by microindentation and nanoindentation systems with Berkovich indenter tips and exhibited enormous increases of several orders of magnitude with decreasing indentation depth. Frank elasticity type molecular interactions were suggested as a rationale for the observed indentation size effect, which could have been related to material models with rotational gradients. A corresponding hardness model yielded good agreement with the experimental data. Other explanations for the indentation size effects in polymers in the literature are discussed in view of these experimentally determined and astonishing hardness increases in PDMS. (C) 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 128: 258-264, 2013