Who says a roof has to be metal?

As automakers review their assumptions about what materials are required for vehicle construction, France's Citroën proposes a new technology for roofs: cardboard. The idea, according to the Stellantis brand, is that roofs typically represent a hefty share of a vehicle's weight. Last year, Citroën unveiled its Oli concept with a roof made of recycled corrugated cardboard it said is strong enough to support the weight of one or two adults. Working with supplier BASF, Citroën created a honeycomb sandwich structure of cardboard between fiberglass reinforcing panels and coated in a polyurethane resin, all of it half the weight of a comparable steel panel roof.