In electrodialysis desalination processes, it is desirable to operate at the highest practicable current density in order to get the maximum ion flux per unit membrane area. The operating current density is limited by concentration polarisation. In this work the development of optimal spacer configurations to decrease concentration polarisation and improve the process performance is presented. Standard non-woven and multi-layer net spacers are tested and their performance in the light of mass transfer enhancement and cross-flow power consumption is evaluated. We utilise multi-layer spacer configurations comprising a standard middle spacer with two thin outside net spacers which result in the highest mass transfer enhancement. When the diameter of the filament of the middle spacer is reduced the same mass transfer enhancement can be reached at 30 times lower cross-flow power consumption. Besides, at the same cross-flow power consumption the developed multi-layer spacer shows 20% higher mass transfer than a standard commercial non-woven net spacer. (c) 2006 Elsevier B.V. All rights reserved.