Most of the CSeries wing, about 80% of it in fact, is composite. Specifically the torque box – the wing’s main strength member – and wing skins are of carbon fibre reinforced plastic (CFRP), as are the moving control surfaces (ailerons, spoilers and flaps). Other CFRP parts include the winglets, fixed trailing edge shrouds and main landing gear doors. However, parts of the internal stiffening structure, notably the ribs, are of aluminium alloy, together with the wing leading edge and slats, while the attachments for the engine pylons are titanium... The metal content illustrates the tendency of designers today to make best use of both composites and metals, separately or in combination, depending on the particular structural requirements...Interestingly, the CSeries wing configuration resembles that of Airbus’ latest design, the A350, similarly having composite spars and envelope plus metal ribs.