Super selective hollow fibre membranes

A hollow fibre membrane has an active layer (2) in which elongate polymer molecules (3) are longitudinally aligned essentially parallel to the extrusion direction to thereby define a plurality of spaced free volume cavities (4) which are particularly numerous and are essentially regularly spaced to provide enhanced selectivity when used in gas separation. The hollow fibre membrane is manufactured using a dry/wet phase separation process by spinning a dope composition which is extruded through a spinneret (12) having an annulus or annular orifice (16) together with a bore-forming fluid or coagulant. The dope composition has a power law index of less than 1 (unity) and the bore coagulant has a water activity of less than 1 (unity).