We intend to construct SixPak, a wide-field fibre-based IFU for the 4.2-meter William Herschel Telescope on La Palma. The fibre bundle will consist of 238 fibres, each 3.0 arcsec in diameter, piping light from the Nasmyth focal plane of the WHT to the existing WYFFOS bench spectrograph. A total of 217 fibres will be densely packed to span a hexagonal field of view of 64 × 55 arcsec. The remaining 21 fibres will collect light from the sky background. SixPak is optimized for 2-dimensional spectroscopy at intermediate resolutions of extended objects of low surface brightness. At Nasmyth focus, a focal reducer matches the f-ratio of the telescope (f/11) to the "optimal" f-ratio of the fibres (f/3) to reduce the losses due to focal ratio degradation in the fibres. Microlenses convert the output f-ratio of the fibres to the f-ratio of the WYFFOS collimator (f/8.2). By means of an exchangeable slit at the pupils of the microlenses, a spectral resolution of R = 10,000 can be achieved. The intention is that SixPak will be open for general use in order to allow easy access to the broadest possible astronomical community.