An element for use in fluid filtration, comprising: (a) a permeate spacer element, permeable to a fluid; (b) a first membrane sheet disposed next to a first surface of the permeate spacer element; (c) a second membrane sheet, permeable to a fluid, disposed next to a second surface, opposite the first surface, of the permeate spacer element; and (c) a feed-reject spacer element (2; 5) mounted on a surface of the first membrane sheet and separated from the permeate spacer element by the first membrane sheet, or mounted on the second membrane sheet and separated from the permeate spacer element by the second membrane sheet, comprising feed-reject spacer features (2; 5) deposited on the surface of the first membrane sheet or the second membrane sheet, where the feed-reject spacer features (2; 5) project from the surface on which they are deposited by a height that increases near a first end of the sheet on which they are deposited to a second height, greater than the first height near a second end, opposite the first end, of the sheet on which they are deposited; wherein, when the permeate spacer element, second membrane sheet, first membrane sheet, and feed-reject spacer element (2; 5) are rolled into a spiral wound element, the permeate spacer element provides a permeate volume between the second membrane sheet and the first membrane sheet, and the feed-reject spacer element (2;5) provides a feed-reject volume between the second membrane sheet and the first membrane sheet; wherein the permeate spacer element, the feed-reject spacer element (2; 5), or both, provide for a separation between the second membrane sheet and the first membrane sheet, which separation changes along the direction of fluid flow in the space between the adjacent sheets when the element is in use for fluid filtration. (a) a permeate spacer element, permeable to a fluid; (b) a first membrane sheet disposed next to a first surface of the permeate spacer element; (c) a second membrane sheet, permeable to a fluid, disposed next to a second surface, opposite the first surface, of the permeate spacer element; and (c) a feed-reject spacer element (2; 5) mounted on a surface of the first membrane sheet and separated from the permeate spacer element by the first membrane sheet, or mounted on the second membrane sheet and separated from the permeate spacer element by the second membrane sheet, comprising feed-reject spacer features (2; 5) deposited on the surface of the first membrane sheet or the second membrane sheet, where the feed-reject spacer features (2; 5) project from the surface on which they are deposited by a height that increases near a first end of the sheet on which they are deposited to a second height, greater than the first height near a second end, opposite the first end, of the sheet on which they are deposited; wherein, when the permeate spacer element, second membrane sheet, first membrane sheet, and feed-reject spacer element (2; 5) are rolled into a spiral wound element, the permeate spacer element provides a permeate volume between the second membrane sheet and the first membrane sheet, and the feed-reject spacer element (2;5) provides a feed-reject volume between the second membrane sheet and the first membrane sheet; wherein the permeate spacer element, the feed-reject spacer element (2; 5), or both, provide for a separation between the second membrane sheet and the first membrane sheet, which separation changes along the direction of fluid flow in the space between the adjacent sheets when the element is in use for fluid filtration.