Goodbye glass? Polycarbonate gains favor
Lightweight material is used increasingly in windows, roofs

Michael LeGault
Automotive News
November 19, 2007 - 12:01 am ET



Automotive glass reached a turning point in 2005.

That year the National Highway Traffic Safety Administration issued a clarification of its regulations for automotive glazing. NHTSA's statement said polycarbonate could be used in windows in place of glass provided it met the same performance standards as glass.

"We sent the NHTSA clarification statement to 19 OEMs around the world," says Exatec LLC CEO John Madej. "It allowed us to get beyond technical and legal questions and focus on vehicle performance."

In 2005 Exatec was running about 30 prototype window programs. That jumped to 275 in 2006.

Polycarbonate is 40 to 50 percent lighter than tempered glass and 50 to 60 percent lighter than laminated glass. Designers have been shaving weight out of every part of the vehicle for decades. Windows, though, have been largely untouched.

Panoramic roofs are a styling trend that plays into polycarbonate's strengths, Madej says. Consumers like them because they allow more light into the vehicle. But designers hesitate to add more roof weight because of the risk of rollovers.

The 2006 Mercedes GL class used a polycarbonate roof panel. Daimler AG's 2008 Smart ForTwo also has a polycarbonate roof. The concept Chevrolet Volt uses polycarbonate in the doors, roof and rear hatch. The roof panel of the Volt was designed with touch controls for interior lighting.

Wade Bryant, General Motors' design manager for advanced interiors, says GM plans to use polycarbonate glazing in two unspecified vehicle programs launching between 2010 and 2012. "Polycarbonate will have a distinct advantage in any future vehicle that needs to achieve weight savings," Bryant says.

Polycarbonate is more expensive than glass. High-volume production runs and greater design flexibility may help lower this cost premium. Bryant praises polycarbonate's "formability."

"You can do channels for lighting, sharp creases and other features in polycarbonate that you can't do in glass," he says.

Exatec's polycarbonate glazing technology can be used for all vehicle window applications except the front windshield. The company has developed a conductive paste that can be used to form the defroster lines on the backlight, replacing wires. Madej says the company is working with a number of automakers on projects that will be commercial after 2010.

He adds: "We know we have to continue to innovate on both the polycarbonate side and the coating side to maximize performance."