Cardboard is a low-cost, virtual reality (VR) headset that transforms an ordinary smartphone into an immersive media viewer. It arrives flat packed in a protective, mailable sleeve, and can be folded and assembled by the user in under a minute. Cardboard is die cut from a single piece of cardboard—it's simple to manufacture industrially and easy to replicate and construct at home. The design templates are freely available on the internet. Cardboard's design is ingenious as it is frugal. A ring magnet on the left side creates a delightful sliding input that requires no physical or electronic connection to the phone. A Near Field Communication (NFC) sticker launches the Cardboard app automatically when a device is inserted. A rubberband keeps the phone from sliding. Cardboard stands out among VR viewers—it's simple, clever, accessible and fun to use.