Rocketbook Cloud Cards 40 pk are reusable index cards built for the digital age. Like all other index cards these are 3” x 5”. Unlike all other index cards Cloud Cards work with the Rocketbook app to be automatically turned into a digital pop quiz for late-night learning or practicing a presentation. Remember the innovative synthetic paper allows you to write smoothly with a Pilot FriXion pen then magically wipe your pages clean with a damp cloth to reuse again and again. With lines on one side and a dot grid on the other Cloud Cards conform to your note-taking needs. So get your head out of the clouds and into the future of index cards!