Similarities and differences between Boom Clay at the HADES Underground Research Laboratory in Mol (Campine, Belgium) and Opalinus Clay at the Mont Terri Rock Laboratory in Saint-Ursanne (Jura, Switzerland): geological setting and burial history (SM-1); petro-physical parameters (SM-2); mineralogical composition (SM-3); porewater characteristics (SM-4); and main transport parameters (SM-5).