The role of solvent evaporation on the crystalline state of electrospun Nylon 6 fibers was examined by electrospinning into a closed chamber filled with different concentrations of solvent vapor. It was found that the thermodynamically stable alpha form became increasingly dominant in Nylon 6 fibers electrospun out of both 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP) and formic acid as the vapor phase solvent concentration increased. It is believed that the formation of the metastable gamma form is due in part to the fast solvent evaporation kinetics associated with the electrospinning process. By varying the vapor phase concentration and thus the rate of solvent evaporation during electrospinning, we were able to vary the resulting crystal structure of the electrospun Nylon 6, as shown by XRD, Raman and FTIR. (C) 2010 Elsevier Ltd. All rights reserved.