Electrospinning uses a high voltage electric field to produce fine fibers. A new phenomenon of self-assembly in the electrospinning of polyurethane nanofibers is observed. This report is the first known self-assembling phenomenon in polyurethane electrospun nanofibers. Electrospun polyurethane nanofibers self-assemble into unique honeycomb patterns on the collector surface. This novel observation opens up new and interesting opportunities for electrospun fibers in the areas of drug delivery devices, protective clothing, filters, and tissue scaffolds. (c) 2006 Wiley Periodicals, Inc.