Pure resole, phenol–formaldehyde was cured under a variety of conditions and evaluated by thermomechanical analysis, swelling studies and 13 C cross-polarization/magic-angle spinning nuclear magnetic resonance spectroscopy. Swelling tests showed that this system has a polymer–solvent interaction parameter in the range 0.92 to 0.99. Measured crosslink densities and glass transition temperatures were found to correlate with proton longitudinal relaxation in the rotating frame, T H 1ρ . Deuterium enrichment was used to show that spin diffusion makes a significant contribution to T H 1ρ . However, the correlations established demonstrate that lattice effects are not obscured. It is shown that deuterium enrichment dilutes the spin system thereby providing a more sensitive probe of motional processes and network cure. These findings establish a method for the evaluation of cured phenol–formaldehyde within a wood-based composite.