Neutron imaging is a nondestructive evaluation technique with enhanced hydrogen sensitivity that allows researchers to monitor water content and transport in materials. In lignocellulosic research, this technique has typically been used to measure changes in moisture content, water transport and even local changes in the density of wood. Yet, studies looking into the combined effects of moisture-uptake, chemical modifications and thermal degradation are still lacking. This is perhaps due to the inherent limited availability of these instruments and their lesser spatial resolution compared to X-ray imaging. While recent advances in detector technology and neutron production have led to continued improvements in both instrument availability and spatial resolution, the technique remains underutilized in forest products research. Here, we used thermal neutron imaging to measure differences in the attenuation of the neutron beam due to acetylation in both solid wood samples and wood−plastic composite samples, as well as a thermally degraded wood sample. Our results show that moisture plays a key role in the contrast. Moreover, we showed that the attenuation coefficient is particularly sensitive to changes in density and/or local hydrogen content caused by thermal degradation of the wood polymers.