A spiral wound filtration element comprising: a central collection tube having at least one hole defined therein; at least one membrane envelope attached to the central collection tube and having two membrane sheets separated by a spacer, the at least one membrane envelope wrapped around the central collection tube to form a spiral; and at least one feed spacer disposed adjacent to at least one membrane sheet when wrapped around the central collection tube and to create a channel to receive liquid to be filtered, the feed spacer comprising a netting including: a first set of parallel strands extending in a first direction and including a plurality of first strands having a first thickness and a plurality of second strands having a second thickness that is smaller than the first thickness; and a second set of parallel strands extending in a second direction that is transverse to the first direction; characterised in that the first set of strands and the second set of strands are always located on the same side of each other; wherein the second set of parallel strands includes a plurality of third strands having a third thickness and a plurality of fourth strands having a fourth thickness that is smaller than the third thickness; and wherein the first set of parallel strands comprises alternating first and second strands and the second set of parallel strands comprises alternating third and fourth strands. a central collection tube having at least one hole defined therein; at least one membrane envelope attached to the central collection tube and having two membrane sheets separated by a spacer, the at least one membrane envelope wrapped around the central collection tube to form a spiral; and at least one feed spacer disposed adjacent to at least one membrane sheet when wrapped around the central collection tube and to create a channel to receive liquid to be filtered, the feed spacer comprising a netting including: a first set of parallel strands extending in a first direction and including a plurality of first strands having a first thickness and a plurality of second strands having a second thickness that is smaller than the first thickness; and a second set of parallel strands extending in a second direction that is transverse to the first direction; characterised in that the first set of strands and the second set of strands are always located on the same side of each other; wherein the second set of parallel strands includes a plurality of third strands having a third thickness and a plurality of fourth strands having a fourth thickness that is smaller than the third thickness; and wherein the first set of parallel strands comprises alternating first and second strands and the second set of parallel strands comprises alternating third and fourth strands. a first set of parallel strands extending in a first direction and including a plurality of first strands having a first thickness and a plurality of second strands having a second thickness that is smaller than the first thickness; and a second set of parallel strands extending in a second direction that is transverse to the first direction; characterised in that the first set of strands and the second set of strands are always located on the same side of each other; wherein the second set of parallel strands includes a plurality of third strands having a third thickness and a plurality of fourth strands having a fourth thickness that is smaller than the third thickness; and wherein the first set of parallel strands comprises alternating first and second strands and the second set of parallel strands comprises alternating third and fourth strands.