The effect of hydration on phase composition, aminoacids side-chain dynamics, and domain thickness of hard alpha-keratin was investigated by H-1 solid-state NMR. Decomposition of wide-line H-1 NMR spectra was used to determine the phase composition and to obtain information on molecular motion. Proton spin-diffusion NMR experiments using a double-quantum dipolar filter were used to estimate the rigid domain sizes for the hydrated Caucasian hair fibres. The relative domain sizes were obtained from the solution of spin-diffusion equation for cylindrical morphologies in the initial-rate approximation by a novel approach. A qualitative model describing the morphological and molecular dynamics changes induced by hydration was developed. (c) 2009 Elsevier B.V. All rights reserved.