A heat transfer assembly is disclosed which comprises at least one wall (1, 2, 3) which is adapted to separate a first fluid at a first temperature from a second fluid at a second temperature, and at least one fiber member (6, 7, 8, 9) or plurality of them, each fibre member (6, 7, 8, 9) including at least one elongate fibre which extends substantially axially along the fiber member (6, 7, 8, 9) from the first fluid through the wall (1, 2, 3) and into the second fluid whereby in use heat is transferred from the first fluid to the second fluid or vice versa, and the entire heat transfer assembly or a part of it is assembled as a single unit by sewing/weaving/stitching technique.