Nanofiber filtration is drawing great interest nowadays because of its large Surface collection area as well as low air resistance In this study, electrospun nanofiber mats different thicknesses were evaluated for their filter quality factors. Shorter-term electrospun fiber mats exhibited a better quality factor than those longer-term electrospun ones Multiple thin layers of nanofiber mats to improve the filter quality of the nanofiber filters were then evaluated. Filtration test results showed that the filter made up of multiple thin layers of nanofiber mats had a filter quality factor much higher than the single thick layer nanofiber mat. Better thickness uniformity in the multi-layer structure due to stacking compensation and smaller fiber diameters in nanofibers short-term deposition time are two possible reasons for the improvement of the filter quality (c) 2009 Elsevier Ltd. All rights reserved