With the twist of a knob, the glass in an experimental VW Touareg sport-utility vehicle goes from clear to dark in one to two seconds. At VW's lab in Palo Alto, it's known as switchable glass. Inside the lab, such glass is used to separate cubicles from a nearby driving simulator.

Rather than photo-sensitive glass — like the lenses found on some sunglasses that take more than a minute to darken in strong light — switchable glass does it almost instantly. It's accomplished using suspended particle devices with a film between two sheets of glass. When it's off, the window is dark. But when an electrical field is applied to the film, the particles align with the field and light shines through.

It offers better comfort and privacy, VW engineers said. Although the Touareg has it in all of its windows except for the front windshield, use in a sunroof might be its initial production application.

— Matt Nauman