Leather is a porous material composed of a three-dimensional weave of collagen fiber bundles. The high pressure tanning (HPT) of sheepskins with valonea tannin in supercritical CO2 was approached to investigate the diffusion process through the skin matrix. Uptake of vegetable tanning agent (VTA) was analyzed at 100 bar and 32 degrees C with varying tanning times (2-8 h). Shrinkage temperature (T-s) as thermal stability of the tanned collagen and filling coefficient (%) of pressurized vegetable tanning (PVT) were also analyzed. The best results were obtained at 8 h treatment yielding 83.77% of VTA uptake and a filling coefficient of 54.97%. PVT experiments showed a satisfactory conversion of the skins to leather in terms of the thermal stability. Scanning electron microscopy (SEM) of the tanned skins showed that high pressure did not alter the fiber structure and morphology negatively. The proposed technique has high potential to be deployed to industrial scale. (C) 2015 Elsevier B.V. All rights reserved.