Abstract: In a process for separating miscible substances by mass transfer between two phases, at least one of which is a fluid phase (gas, vapor or liquid) and the other phase being a solid phase or a liquid phase (stationary or flowing in countercurrent with the aforesaid fluid phase, the mass transfer takes place and is substantially confined to the outside of the surface regions of the solid parts of porous material having the structure of an open pore foam, preferably substantially reticulated. This structure can be industrially reproduced in an idealized fashion in the form of interleading pores between which the solid parts are outlined in all three dimensions by concave shapes of spherical to near-spherical curvature corresponding to the outlines of densely packed phases.Column packings for chromotography, distillation, countercurrent extraction and similar process.