Duralumin (or duraluminum) is an alloy of aluminium (about 95%), copper (about 4%), and small amounts of magnesium (0.5%–1%) and manganese (less than 1%). It is considerably stronger than elemental aluminium, and more resistant to corrosion. This alloy also adds considerable tensile strength to normal aluminium, which otherwise "rips" quite easily.

With this new rip-resistant mixture, duralumin quickly spread throughout the aircraft industry in the early 1930s, where it was well suited to the new monocoque construction techniques that were being introduced at the same time. Duralumin also is popular for use in precision tools such as levels because of its light weight and strength. Today almost all material that claims to be aluminium is actually an alloy thereof. Pure aluminum is infrequently encountered.