A membrane spacer comprising two or more sub-spacers (32). The at least one sub-spacer includes an inlet aperture and an outlet aperture (20) where the inlet aperture connected to the outlet aperture by a substantially curved flow path. The substantially curved flow path includes a plurality of grid sectors (23) running perpendicular to the curved flow path. The two or more sub-spacers (32) are aligned to provide a tortuous flow path between the inlet aperture and the outlet aperture (20).
