That's weird, the lens I got was definitely dual pane :OThe spare lens from 09 vents is single, and crap. In fact, you used to be able to send them back and get new ones, as the anti-scratch coating comes off without ever using the mask. I had to give a bunch of free clear lenses away, but Kee did replace them for me.
In short, it's a single, and not a good one. You'll need a lens.
Then again it was packaged separately to the goggles when I got it as though it was an individual product