A pane is a sheet of glass, so a double pane window would have 2 sheets of glass, whereas a single pane would have one. You are talking about cars right, not houses? In cars a double pane would be heavier, but block sound better, the single pane would be lighter but allow more noise to come through. I think the only NSX to come to America with a single pane window was the Zanardi edition. The bulk head window was single pane. If you want to save some pounds (glass is pretty heavy, but we are talking about a small window) and would like/wouldn't mind a little more engine noise, then by all means switch.