Top and bottom are aluminum but the sides are Polycarbonte
I have talked with a reviewer that used the XZ Premium yesterday to the Sony event in Lisbon. Finally, the lateral frame (the two lateral sections) are in PLASTIC (polycarbonate)...!!!
The back of Xperia XZ Premium is made from Corning Gorilla Glass 5, the display is made from Corning Gorilla Glass 5, and the frame from Nylon.