http://www.techradar.com/news/apple-might-move-back-to-metal-for-one-iphone-9-model

The iPhone 8, iPhone 8 Plus and iPhone X all have glass backs, having moved away from the metal rears of past generations, but according to a source at least one of 2018’s models might switch back to a metal rear.

Speaking to Nikkei, the source, who’s apparently “privy to the company’s product designs”, said that Apple will launch a 6.1-inch LCD phone that will “probably” have a metal back available in several colors.