This paper gives a general overview of hygro-thermal characterization of bio-based building materials. Because of the coupling between heat and mass transfer, experimentation and modeling must be used in synergy. For example, any measurement devoted to mass transfer properties needs to be analyzed by a relevant physical model accounting for this coupling. Em-phasis will also be put on the complex issue of liquid migration. Finally, upscaling is introduced as an additional way to obtain macroscopic behav-iors from the 3D morphology and the phase properties of a heterogeneous material.