A porous fluoropolymer membrane comprising a first surface, a second surface, nodes and free fibrils, wherein one of the first and second surfaces has a greater number of free fibrils per unit area of the surface than the other of the first and second surfaces, is disclosed. A process for preparing porous fluoropolymer membranes is also disclosed, comprising splitting a thicker membrane in a dimension different from, e.g., perpendicular to, its thickness dimension.