The three-dimensional (3D) microstructure of sustainable and biodegradable protein foam absorbents is correlated to their liquid absorption characteristics using X-ray microtomography. The physicochemical relationships between the protein material pore size and liquid penetration and distribution allow for understanding how the pores' interconnectivity impacts the absorption, particularly considering capillary-driven transport phenomena within the thin nano cell walls. The foams were made via lyophilization of protein solutions containing cellulose nanofibers to emphasize the impact of the processing on the foam microstructure. The results show gaseous and solid phases of the foams covering ca. 1000 pores, providing information that cannot be obtained using traditional 2D analysis (SEM). A correlation with the channel tortuosity was established based on the statistical ac-curacy of the diameter and number of pores per mm(3). The relationship between absorption kinetics and physical parameters enables the designing of biofoams with functionality also resembling commercial synthetic products that currently generate a high amount of nondegradable waste in our society.