Apple has been working on a foldable display for use on a smartphone since at least 2014, a newly published patent has revealed.

The patent, filmed in July 2014 and made public on 22 November, describes a flexible OLED screen installed onto a folding metal structure. The screen can be folded fully in half, closing in on itself like a 1990s Motorola flip-phone.

Although Apple doesn't specifically say the foldable screen will appear on a future iPhone or iPad, the patent, discovered by AppleInsider, shows how an upper and lower housing either side of the display (when folded shut) could contain processors, sensors, cameras and other smartphone components like a vibration motor, battery, microphone and speakers.

One description shows how the device can be made to include sawtooth edges for clipping into a user's clothing. Another shows how the device could feature two hinges, bending the display in two different directions.

This is just one of several Apple patents relating to the development of flexible displays. In early November the US patent office described a device with a central hinge allowing it to be folded in half like a book.

The patent was awarded to Apple by the USPTO (United States Patent and Trademark Office) on 1 November, and describes a device built from ceramic, glass, aluminium or plastic and containing both rigid and flexible portions. More significant is the described use of carbon nanotubes, which would allow the device to flex while remaining functional.

As always with patent stories, it is commonplace for technology companies to experiment with many different designs and manufacturing processes. Although Apple is clearly interested in flexible screens, it is very unlikely that we will see an iPhone with a display like this any time soon. However, similar technology could be implemented on future MacBooks, iPads or even an entirely new product category, such as a new wearable device.