Through all of the leaks of the Huawei-made Nexus 6P, everyone has wondered what the black bar on the back is for and why it's there. Since the Huawei Nexus 6P is all aluminum, and as many of you likely know it's tough for signal to penetrate aluminum unibody device, therefore all of those sensors all live in that black bar at the top. This includes the NFC chip, WiFi, Bluetooth, GPS and just about anything else you can think of. It's great to put NFC up there because it makes Android Pay even easier to use, because you know where the NFC chip is. Apple actually did the same thing with the iPhone 6, 6 Plus, 6S, and 6S Plus, to make it easier to use Apple Pay.
The black bar there is actually glass, and it does also house the camera, dual-flash and laser auto-focus. The glass used on the bar is actually Gorilla Glass 4, so it should be fine, and not get scratched up at all, like many will be afraid of. This info actually came directly from Google. Actually from a person working on the design of the Nexus 6P as well as the Nexus 5X.
To be honest, this info makes a whole lot of sense. It serves a ton of purposes. One, it keeps Google from need to add lines in the frame to allow the antennas to get a signal out. Two, it makes it easier for users to use Android Pay, seeing as it uses NFC and we don't always know where the NFC chip is, it makes it much, much easier. Three, better Bluetooth and GPS signal. We've all had issues with GPS and Bluetooth issues on smartphones with an aluminum unibody, and designing the Nexus 6P this way solves that issue. Great idea Google and Huawei.
So while the black bar there on the back may not be the best looking part of the new Nexus 6P, it does serve a purpose, and one you'll more than likely appreciate after using the phone for a while. It also explains why the different color Nexus 6P models don't have a different bar up there at the top.