The next Audi A3 will be almost as light as the original model from 1996, despite having significantly more safety and luxury features.
Audi sees weight-saving as one of its 'core competences' and a vital part of its emissions-reducing programme.
"With this model we have broken through the weight spiral while adding to safety and equipment," said Dr Olaf Kohler, responsible for the car's lightweight engineering.
The weight reduction is as much 80kg on at least one model, even though the exterior dimensions of the new model are roughly the same as those of the current, second-generation car.
The automaker claimed to have examined every single component to see if weight could be trimmed. The new generation has a 'multi-material body', including lightweight steels and an aluminium bonnet and bumper supports, which saved 18kg.
There is a new aluminium front subframe (6kg off) and lighter sound deadening materials in the cabin. The seats, air conditioning, wiring and plastics are lighter. Even the metal screws which hold parts of the interior trim together have been replaced by plastic rivets.
This will be the first car to be built on the Volkswagen group's new modular transverse platform which will eventually underpin everything from the Polo through Golf to the Passat, A1 and A3 family and almost every Skoda and Seat. This is another great help towards weight reduction, said Kohler.
But the biggest single saving is the 21kg reduction achieved by the new 1.4-litre TFSI petrol engine which will be the entry-level power unit at launch in September. There will also be new 1.8TFSI and two-litre TDI turbodiesel units. CO2 emissions are down to as low as 120g/km for the petrol engines and 99g/km for the diesel.
Later will come 1.2-litre petrol, 1.6-litre diesel, high-performance 'S' and electric versions.
Audi has used lightweight body technology since 1994's A8 built around its ASF (aluminium space-frame) architecture, 40% lighter than a conventional steel body though it does require specialist repair skills and equipment.
Production of successive generations of the A8, and the R8 sports cars built along similar lines, has now topped 700,000 units.