Electrospinning is a process to generate a nanofibrous material. Although the working principle of electrospinning is rather straight forward, it is influenced by many parameters. There is still a serious lack of knowledge concerning the influence of the ambient parameters, for which preliminary knowledge reveals that the relative humidity is of primary importance. This article reports the influence of the relative humidity on electrospun polyamide 6 nanofibres. Mixtures of formic acid and acetic acid are used for steady state electrospinning of polyamide 6 nanofibres, for which a steady state table is determined. When the relative humidity increases, the average fiber diameter decreases and the fraction of the less stable c-phase crystals in the polyamide diminishes. This effect is explained by absorbed water acting as a plasticizer, reducing the Tg of the polyamide. This article shows the importance of working in climatized conditions during electrospinning to obtain reproducible nanofibres. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 119: 2984-2990, 2011