Hollow Porous Fibers

A method for forming a hollow fiber, the method comprising:

• forming a thermoplastic composition that contains a continuous phase that includes a matrix polymer and a nanoinclusion additive dispersed within the continuous phase in the form of discrete domains;
• extruding the composition through a capillary to form the fiber, wherein one or more shaped slots are positioned within the capillary;
• and
• drawing the fiber at a temperature that is lower than the melting temperature of the matrix polymer, thereby forming a porous network that includes a plurality of nanopores,
• wherein the hollow fiber comprises a hollow cavity that extends along at least a portion of the fiber in the longitudinal direction, wherein the cavity is defined by an interior wall having an average wall thickness of from about 0.5 to about 50 micrometers.