Do car windows protect skin from sunburn?

Automotive glass must meet a host of safety standards, but there are no requirements for sun protection. That can vary by vehicle, and even by window within a vehicle.

Windshields offer the most sun protection, according to Pete Dishart, who leads product development at Pittsburgh Glass Works in Pennsylvania. His company supplies glass to nearly every major automaker.

Under federal Department of Transportation motor vehicle safety standards and regulations, windshields are made of laminated glass, including a layer of plastic. Plastic is good at absorbing UV rays, Dishart says, and can be made with extra UV absorbers to protect even more. He says windshields absorb 100 percent of UVB rays, which cause sunburn, and around 98 percent of UVA rays, which don’t cause sunburn but can do long-term skin damage.

That gives windshields a sun protection factor - or SPF - of 50 or more, the equivalent of some of the strongest sunscreens, Dishart said.

Sunroofs, too, often contain UV-absorbing technology that can block around 90 percent of UV rays.

But side and rear windows are a different story, and their SPF can vary a lot depending on the vehicle.

Side windows are usually made from cheaper tempered glass, which is around 4 millimeters thick and doesn’t include a layer of plastic. Tempered glass is designed to shatter into tiny pieces, to protect the occupants in a crash. But unless they’re tinted for privacy, side windows usually absorb only 65 percent of UV rays. That gives them an SPF of around 16, Dishart says, the same as some of the lowest grades of sunscreen.

Some automakers are opting for more expensive, higher-SPF glass, to both protect the car’s occupants and to keep car interiors cooler.

ActiveStyle, Pages 29 on 09/09/2013