Polypropylene hollow fibers were produced via the spunbonding process. Nitrogen gas was used as the lumen fluid. The polypropylene continuity equation can be combined with the nitrogen continuity equation to give excellent predictions of the inside diameter and the outside diameter of the product fiber. Tests were developed to measure the compression-recovery behavior of hollow fiber mats (nonwoven structures) versus mats of solid fibers. Tests were also developed to measure the opacity of hollow fiber mats versus solid fiber mats. In terms of compression-recovery and opacity, mats of hollow fibers are nearly identical to mats of solid fibers of the same outside diameter.