Even though TCL, Oppo and LG have been teasing the rollable phone form factor for some time now, none of them have launched one just yet. The next best thing for now is Oppo's working prototype, three of which arrived in Hong Kong recently, so naturally, we went to take a closer look at this rare device. The idea of the Oppo X 2021 is to let you switch between a conventional 6.7-inch screen and a mini-tablet-like 7.4-inch screen, with the former offering better portability, and the latter a better experience for videos, reading, gaming and multi-tasking. This is achieved by rolling part of the flexible OLED panel into the back of the phone, which supposedly avoids the creasing issue we've seen on foldables. The screen rolling is toggled via the power button: a double click or swipe-up extends the screen, and another double click or swipe-down retracts it. This sliding movement is powered by two motors, which push and pull the two halves of the body. The flexible panel is fixed to the right side, before entering a gap on the left and tucked around a roller with a 6.8mm diameter. The flexible screen is surprisingly tough. This is partly thanks to the "2-in-1 plate" comb-like sliding structure underneath, which provides a rigid structure in both phone mode and tablet mode. In addition, the OLED panel itself is reinforced by a thin caterpillar track laminate consisting of steel parts, which apparently improved the overall strength while still keeping it flexible. As a concept device, the Oppo X 2021 is surprisingly usable. That said, this prototype was missing a couple of essential features: volume keys and selfie camera. Chances are Oppo left those out to help speed up development, and it'd most likely add those back before launching the device, if it ever does. Despite the Oppo X 2021's second public appearance last month, the company still doesn't plan on mass-producing it. But as far as proof of concept goes, the rollable phone future is looking promising, save for the small kinks here and there. Read our full hands-on with the Oppo X 2021 prototype here: https://www.engadget.com/oppo-x-2021-hk-hands-on-071842802-175042576.html Subscribe: null Like us on Facebook: http://www.facebook.com/engadget Follow us on Twitter: http://www.twitter.com/engadget Follow us on Instagram: http://www.instagram.com/engadget Follow us on TikTok: https://www.tiktok.com/@engadget The Engadget Podcast: https://itunes.apple.com/us/podcast/the-engadget-podcast/id1142790530?mt=2 More about Engadget Audio: https://www.engadget.com/2019-08-01-engadget-podcasts.html Read more: http://www.engadget.com/