The present invention relates to a membrane being suitable for, for example, hemodialysis. Said membrane comprises at least one hydrophobic polymer and at least one hydrophilic polymer. According to the present invention the outer surface of the hollow fiber has pores in the range of 0.5-3 μm and the numbers of said pores in the outer surface are in the range of 10,000 to 150,000 pores per mm2, preferably in the range of 18,000 to 100,000 pores per mm2, and most preferably in the range of 20,000 to 100,000 pores per mm2. The present invention further relates to a process for the preparation of said membrane and use of said membrane in hemodialysis, hemodiafiltration and hemofiltration, and in dialysis and filtration in general, for example in water purification or dehydration.