Results on direct contact membrane distillation experiments are given. The experiments were carried out to measure the effect on flux of improving the mass transfer characteristics of the membrane used and of including a spacer in the channels of the membrane module used. It is shown that the benefits of membrane mass transfer improvements can be overshadowed if the transfer in liquid phases is not good and that the benefits of spacer inclusion are higher as the polarization effects are higher. If good flux performance is targeted, both membrane and module characteristics must be adequate.