A method for forming porous fibers is provided. The fibers are formed from a thermoplastic composition containing a continuous phase, which includes a matrix polymer, and a nanoinclusion additive that is at least partially incompatible with the matrix polymer so that it becomes dispersed within the continuous phase as discrete nano-scale phase domains. The method generally includes traversing a bundle of the fibers over one or more draw bars that are in contact with a fluidic medium (e.g., water). In certain embodiments, for example, the draw bar(s) are submerged in the fluidic medium. The fluidic medium is lower than the melting temperature of the matrix polymer.