Traditionally, car windows have been made from laminated glass.
It's strong, shatter-resistant, and... err... transparent. Obviously. But it's also rather heavy, and as increasingly weight-conscious car manufacturers are looking for ways to shed weight, glass could now be on the diet list.
While polycarbonate has been used for some time in race cars, as well as more recently in some performance road cars, it's now set to appear on the humble 2014 Fiat 500L wagon, to help cut weight.
Glass can make up 100 pounds of a car's weight, but its equivalent in polycarbonate could be half that.
It wouldn't be used throughout, instead seeing service in rear windows or sunroofs, reducing weight where appropriate.
It could realistically be used for side windows, but there's a safety issue here. Not that the plastic is too weak, but that it's too strong--in an accident, first responders would have trouble breaking through to injured or trapped occupants. As a result, they're prohibited for use as windscreens or side windows.
Scratch resistance, hazing and cost are all cited as potential stumbling blocks. UV-protecting layers can prevent hazing under years of sunlight (something you can often see on older polycarbonate headlamps) but additional layers would be required to prevent scratching.
Polycarbonate windows can also be twice the cost of glass windows, though price could come down if the technology is more widely adopted.
Ford is just one company currently running trials, and is near to completing a 10,000-hour environmental durability testing cycle on the windows--if successful, polycarbonate windows could appear in the new Transit Connect due later in 2013.
[UPDATE: Ford spokesman Mike Levine later contacted Green Car Reports regarding the sentence above, saying that Ford has no plans to use plastic windows in the upcoming 2014 Ford Transit Connect--a fact subsequently changed in the article from The Detroit News that was originally cited by our author.]
There's another benefit of the windows, despite the extra cost: Design.
Compression moulding techniques allow the plastic to be formed into all manner of shapes much more easily than glass. Windows could be even formed into aerodynamic shapes themselves, without compromising strength or increasing complexity.
The cool hexagonal sunroofs on the Kia Cross GT concept launched at Chicago? Not difficult at all to produce in polycarbonate.
It's unclear as to how many cars will use polycarbonate windows, though it's likely to be one facet of the myriad techniques used to reduce weight in future cars.