An airfoil comprising: leading and trailing edges (20, 22); a first exterior wall extending from the leading edge to the trailing edge and having inner and outer surfaces; a second exterior wall extending from the leading edge to the trailing edge generally opposite the first exterior wall and having inner and outer surfaces, wherein the trailing edge is positioned downstream from the leading edge along a direction of air configured to flow along the outer surfaces of the first and second exterior walls (24, 26); a first cavity extending along the inner surface of the first exterior wall and a first inner wall, the first cavity having an upstream end and a downstream end; a second cavity extending along the inner surface of the second exterior wall and a second inner wall, the second cavity having an upstream end and a downstream end; and a feed cavity centrally located between the first inner wall and the second inner wall, wherein the second inner wall separates the second cavity from the feed cavity; characterised in that: the first cavity comprises a first plenum near the upstream end of the first cavity, a first region near the downstream end of the first cavity opposite the first plenum for receiving a cooling fluid, and a first intermediate section joining the first plenum to the first region, wherein the first plenum and the first region have a lateral thickness greater than the first intermediate section; the second cavity comprises a second plenum near the upstream end of the second cavity, a second region near the downstream end of the second cavity opposite the second plenum for receiving a cooling fluid, and a second intermediate section joining the second plenum to the second region, wherein the second plenum and the second region have a lateral thickness greater than the second intermediate section; and the airfoil comprises: a first plurality of cooling holes extending through the first exterior wall and in communication with the first plenum; and a second plurality of cooling holes extending through the second exterior wall and in communication with the second plenum. leading and trailing edges (20, 22); a first exterior wall extending from the leading edge to the trailing edge and having inner and outer surfaces; a second exterior wall extending from the leading edge to the trailing edge generally opposite the first exterior wall and having inner and outer surfaces, wherein the trailing edge is positioned downstream from the leading edge along a direction of air configured to flow along the outer surfaces of the first and second exterior walls (24, 26); a first cavity extending along the inner surface of the first exterior wall and a first inner wall, the first cavity having an upstream end and a downstream end; a second cavity extending along the inner surface of the second exterior wall and a second inner wall, the second cavity having an upstream end and a downstream end; and a feed cavity centrally located between the first inner wall and the second inner wall, wherein the second inner wall separates the second cavity from the feed cavity; characterised in that: the first cavity comprises a first plenum near the upstream end of the first cavity, a first region near the downstream end of the first cavity opposite the first plenum for receiving a cooling fluid, and a first intermediate section joining the first plenum to the first region, wherein the first plenum and the first region have a lateral thickness greater than the first intermediate section; the second cavity comprises a second plenum near the upstream end of the second cavity, a second region near the downstream end of the second cavity opposite the second plenum for receiving a cooling fluid, and a second intermediate section joining the second plenum to the second region, wherein the second plenum and the second region have a lateral thickness greater than the second intermediate section; and the airfoil comprises: a first plurality of cooling holes extending through the first exterior wall and in communication with the first plenum; and a second plurality of cooling holes extending through the second exterior wall and in communication with the second plenum. the first cavity comprises a first plenum near the upstream end of the first cavity, a first region near the downstream end of the first cavity opposite the first plenum for receiving a cooling fluid, and a first intermediate section joining the first plenum to the first region, wherein the first plenum and the first region have a lateral thickness greater than the first intermediate section; the second cavity comprises a second plenum near the upstream end of the second cavity, a second region near the downstream end of the second cavity opposite the second plenum for receiving a cooling fluid, and a second intermediate section joining the second plenum to the second region, wherein the second plenum and the second region have a lateral thickness greater than the second intermediate section; and the airfoil comprises: a first plurality of cooling holes extending through the first exterior wall and in communication with the first plenum; and a second plurality of cooling holes extending through the second exterior wall and in communication with the second plenum. a first plurality of cooling holes extending through the first exterior wall and in communication with the first plenum; and a second plurality of cooling holes extending through the second exterior wall and in communication with the second plenum.