Nano-supersolid T_N depression – supercooling.^[48,53] Skin supersolidity takes the full responsibility for (a) water skin toughness, ice slipperiness, and (b) droplet-size and surface-curvature (inset) resolved T_N depression (called supercooling).^[106,112] Droplet of slightly more-curved surface freezes 68.4 s later at 269 K than the contrast deposited on smooth Ag surface.^[111]