An airfoil comprising: an airfoil wall defining a leading end, a trailing end, a first side wall, and a second side wall; and first and second ribs (64a, 64b) each connect the first and second side walls (62c, 62d) of the airfoil wall, each of the ribs (64a, 64b) including: a first arm by which the respective first or second rib (64a, 64b) is solely joined to one of the first or second side walls (62c, 62d), and second and third arms (68, 70) by which the respective first or second rib (64a, 64b) is solely connected to the other of the first or second side walls (62c, 62d); and wherein for each rib the first arm, the second arm, and the third arm each include a first end (66a, 68a 70a) and a second end (66b, 68b, 70b), the first end of the first arm is attached to one of the first and second side walls (62c, 62d), the second end of the first arm is attached at a node to the respective first ends (68a, 70a) of the second and third arms (68, 70), the second ends (68b, 70b) of the second and third arms (68, 70) are attached to the other of the first and second side walls (62c, 62d), wherein the first end of the first arm of the first rib is attached to one of the side walls (62c, 62d), and the first end of the first arm of the second rib is attached to the other of the side walls (62c, 62d), characterized in that: there is a cooling channel 174 between adjacent first and second ribs (64a, 64b), and the cooling channel has a Z-shape. an airfoil wall defining a leading end, a trailing end, a first side wall, and a second side wall; and first and second ribs (64a, 64b) each connect the first and second side walls (62c, 62d) of the airfoil wall, each of the ribs (64a, 64b) including: a first arm by which the respective first or second rib (64a, 64b) is solely joined to one of the first or second side walls (62c, 62d), and second and third arms (68, 70) by which the respective first or second rib (64a, 64b) is solely connected to the other of the first or second side walls (62c, 62d); and wherein for each rib the first arm, the second arm, and the third arm each include a first end (66a, 68a 70a) and a second end (66b, 68b, 70b), the first end of the first arm is attached to one of the first and second side walls (62c, 62d), the second end of the first arm is attached at a node to the respective first ends (68a, 70a) of the second and third arms (68, 70), the second ends (68b, 70b) of the second and third arms (68, 70) are attached to the other of the first and second side walls (62c, 62d), wherein a first arm by which the respective first or second rib (64a, 64b) is solely joined to one of the first or second side walls (62c, 62d), and second and third arms (68, 70) by which the respective first or second rib (64a, 64b) is solely connected to the other of the first or second side walls (62c, 62d); and wherein for each rib the first arm, the second arm, and the third arm each include a first end (66a, 68a 70a) and a second end (66b, 68b, 70b), the first end of the first arm is attached to one of the first and second side walls (62c, 62d), the second end of the first arm is attached at a node to the respective first ends (68a, 70a) of the second and third arms (68, 70), the second ends (68b, 70b) of the second and third arms (68, 70) are attached to the other of the first and second side walls (62c, 62d), wherein the first end of the first arm of the first rib is attached to one of the side walls (62c, 62d), and the first end of the first arm of the second rib is attached to the other of the side walls (62c, 62d), characterized in that: there is a cooling channel 174 between adjacent first and second ribs (64a, 64b), and the cooling channel has a Z-shape.