One of the most interesting things about the Pixel 5 is that despite coming with an aluminium back, it features wireless charging as well as reverse wireless charging. Every other smartphone featuring wireless charging ships with glass as it is not possible to add wireless charging to a metal phone. So how exactly did Google manage to add wireless charging to the Pixel 5 in spite of its metal build? Well, smartly.
Google has revealed to certain press members that the metal body of the Pixel 5 has a window cut into its backside where the charging coil is embedded. This is then coated with a "bio-resin" for a uniform look and finish and to prevent the charging coil from any damage.
Google is using a Bio-resin on top of the aluminum of the Pixel 5's body to achieve wireless charging. Basically, there is a physical cutout in the aluminum where the coil lives, and this plastic bio-resin sits on top.— David ImeI (@DurvidImel) September 30, 2020
The implementation is pretty smart from Google and for now, it seems there's no side effect to it as well as the Pixel 5 supports up to 10W wireless charging along with wireless charging. How this "bio-resin" coating will hold up over long term use is something that only time will tell. This is not the first time that any smartphone company has done this though. LG did this back in the day but in recent years, OEMs have switched to glass panels to offer wireless charging on their devices.
So why did not Google just use a glass back on the Pixel 5? Well as per the company, the aluminum frame and the "bio-resin" coating allowed it to maintain a relatively slim profile for the device while still managing to fit a relatively large 4,080mAh battery.
Source: Android Authority