Moisture as a Plasticity Switch in Blowouts: Glass-Transition Behavior, Viscoelastic Response, and Tension-Defined Shape

This review explores the role of moisture as a plasticity switch in hair blowouts, highlighting how water acts as a plasticizer for the keratin matrix in human hair. It lowers the glass-transition temperature (Tg) from 144 °C when dry to near ambient temperature when fully hydrated. This transition allows the hair matrix to shift from a rigid to a flexible state, enabling reshaping under tension. As moisture evaporates during blow-drying, the matrix re-vitrifies, solidifying the new shape through a reorganized hydrogen-bond network. The study integrates glass-transition theory, viscoelastic relaxation, and bond reorganization to explain hair shaping as a function of both heat and moisture gradients.