With tough new fuel-economy regulations looming on the horizon and hybrid-electric propulsion systems adding hundreds of pounds to a vehicle, auto makers know they have to put their cars and trucks on a diet, but exactly how remains unclear.

In spite of their higher costs, new materials are the basic approach. But what won't work is eliminating vehicle content, says Michael Vitek, director of North American consulting for Daimler AG consulting subsidiary MBTech.

Consumers who want a hybrid-electric vehicle demand all the regular features of a modern car, he says. Speakers at a recent automotive conference in Traverse City, MI, suggest a mixed menu, different from the fad diets of previous years that stressed one material or another, such as aluminum or plastics.

“We are about at the zenith“ of car mass, and future vehicles will be about the same size as their predecessors, Chrysler LLC designer Ralph Gilles tells reporters.

Brad Dunstan, CEO of Australia's Victorian Center for Advanced Materials Mfg., says changes in the aerospace industry likely will have an impact on the price and availability of lightweight materials for the auto industry in the future.

The Airbus A380 will be the last aluminum-intensive airliner in production, he says, as the commercial aerospace industry shifts to more carbon fiber-intensive aircraft, such as the Boeing 787.

That will free up aluminum capacity and likely drive an automotive marketing effort by aluminum producers.

Meanwhile, Dunstan says the burgeoning popularity of the carbon fiber-intensive Boeing 787 will drive up carbon fiber prices, because as much as 25% of the world's carbon fiber production will be devoted to that aircraft, alone.

Despite the high cost of the material, as well as production and surface finish issues, carbon fiber still has viable automotive applications. It is 75% lighter than steel and has a race-proven ability to enhance crashworthiness, Dunstan says.

Michael Bull, director of technology-automotive at Novelis Corp., says aluminum is alive and well in the auto industry. He points to aluminum-intensive vehicles such as the new Audi TT and Jaguar XK coupe.

But he says the high-volume future of aluminum likely will be in vehicles that use a multi-material approach that combines aluminum with steel. New joining processes involving laser brazing and adhesives are fueling these applications.

Auto makers need to start computing the value of weight-saving materials differently, Bull says. That means including so-called secondary weight savings that lighter parts and body structures enable.

Steel makers are pushing weight-reducing high-strength and ultra high-strength steels to reduce vehicle mass.