A heat exchanger for cooling a first fluid using a second fluid, said heat exchanger comprising: at least one inner heat exchange tube (1000, 1401) for exchanging heat between said first fluid and said second fluid, said at least one inner heat exchange tube having an inner surface and an outer surface; a tubular outer body (112, 1202, 1205) surrounding at least part of said at least one inner heat exchange tube (1000, 1401), said tubular outer body having an inner surface and an outer surface; wherein the first fluid flows through the at least one inner heat exchange tube (1000, 1401) and the second fluid flows between the outer surface of the inner heat exchange tube and the inner surface of the tubular outer body (112, 1202, 1205); and a substantially cylindrical corrugated sheet of material forming a plurality of fins configured for orientation within said at least one inner heat exchange tube (1000, 1401), wherein at least one of said plurality of fins is in contact with the inner surface of the at least one inner heat exchange tube characterised in that: a particular fin of said plurality of fins comprises: an outer connecting wall positioned adjacent to the inner surface of said at least one inner heat exchange tube (1000, 1401), said outer connecting wall having a pair of opposing ends, a pair of substantially straight fin walls (602, 607) extending radially inwardly from the opposing ends of said outer connecting wall, respectively, each of said straight fin walls (602, 607) converging toward a central axis of said at least one inner heat exchange tube, and a gap positioned within said outer connecting wall, said gap having been formed between a first end and a second end of a single elongate strip of material, wherein such single elongate strip of material is folded to form said substantially cylindrical corrugated sheet of material, such that said first end, said gap and said second end collectively form the outer connecting wall. at least one inner heat exchange tube (1000, 1401) for exchanging heat between said first fluid and said second fluid, said at least one inner heat exchange tube having an inner surface and an outer surface; a tubular outer body (112, 1202, 1205) surrounding at least part of said at least one inner heat exchange tube (1000, 1401), said tubular outer body having an inner surface and an outer surface; wherein the first fluid flows through the at least one inner heat exchange tube (1000, 1401) and the second fluid flows between the outer surface of the inner heat exchange tube and the inner surface of the tubular outer body (112, 1202, 1205); and a substantially cylindrical corrugated sheet of material forming a plurality of fins configured for orientation within said at least one inner heat exchange tube (1000, 1401), wherein at least one of said plurality of fins is in contact with the inner surface of the at least one inner heat exchange tube characterised in that: a particular fin of said plurality of fins comprises: an outer connecting wall positioned adjacent to the inner surface of said at least one inner heat exchange tube (1000, 1401), said outer connecting wall having a pair of opposing ends, a pair of substantially straight fin walls (602, 607) extending radially inwardly from the opposing ends of said outer connecting wall, respectively, each of said straight fin walls (602, 607) converging toward a central axis of said at least one inner heat exchange tube, and a gap positioned within said outer connecting wall, said gap having been formed between a first end and a second end of a single elongate strip of material, wherein such single elongate strip of material is folded to form said substantially cylindrical corrugated sheet of material, such that said first end, said gap and said second end collectively form the outer connecting wall. an outer connecting wall positioned adjacent to the inner surface of said at least one inner heat exchange tube (1000, 1401), said outer connecting wall having a pair of opposing ends, a pair of substantially straight fin walls (602, 607) extending radially inwardly from the opposing ends of said outer connecting wall, respectively, each of said straight fin walls (602, 607) converging toward a central axis of said at least one inner heat exchange tube, and a gap positioned within said outer connecting wall, said gap having been formed between a first end and a second end of a single elongate strip of material, wherein such single elongate strip of material is folded to form said substantially cylindrical corrugated sheet of material, such that said first end, said gap and said second end collectively form the outer connecting wall.