While most of the fuselage is made of aluminium alloys, composite materials comprise more than 20% of the A380's airframe. Carbon-fibre reinforced plastic, glass-fibre reinforced plastic and quartz-fibre reinforced plastic are used extensively in wings, fuselage sections (such as the undercarriage and rear end of fuselage), tail surfaces, and doors. The A380 is the first commercial airliner to have a central wing box made of carbon–fibre reinforced plastic. It is also the first to have a smoothly contoured wing cross–section. The wings of other commercial airliners are partitioned span-wise into sections. This flowing continuous cross section reduces aerodynamic drag. Thermoplastics are used in the leading edges of the slats.