The invention disclosed relates to feed spacers used in various filtration membrane modules, such as in spiral wound membranes, used in cross-flow filtration. Such spacers have an influence in promoting the mixing between the bulk of the fluid and the fluid element adjacent to the membrane surface so as to keep the membrane surface relatively clean. To optimize these properties, novel spacer designs are disclosed having a plurality of rows of elongated strands, the strands in each row being arranged substantially in parallel to one another, with adjacent rows being attached and disposed at an angle to one another, the strands of at least one row when viewed in cross-section having a central portion of a width smaller than the width of its extremities. Novel membrane modules incorporating such feed spacers are also disclosed.