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.