Is it free?

Yes. The cost of postage is offset with the help of relevant, targeted, unobtrusive advertisements, which will appear on the back of your Gmail Paper prints in red, bold, 36 pt Helvetica. No pop-ups, no flashy animations—these are physically impossible in the paper medium.

Cómo ignorar y destrozar los avances tecnológicos de los últimos 20 años en 3 cómodos pasos: Gmail Paper.