H–O stiffness transition from the bulk to the skins of large volumes and nanodroplets.^[53,74] (a) Skins of 298 K water and (253–258) K ice^[65] share an identical ω_H of 3450 cm⁻¹ and the (b) D–O phonon^[33] transits from below 2550 to its above for the skin of droplet. Insets show ice slipperiness, water skin toughness, and the elasticity and hydrophobicity of skins of droplet and water.