The rails are plastic but they're thick and seem sturdy, and they don't flex. The end part is metal, and the shell is thick metal, and when you screw it together it feels very solid. (The rails are in a bit of tension holding the end cap in place, but once it's there, there's metal to metal contact between the end cap and bottom shell, screwed together, and between the bottom & top part, in contact, and it feels very solid. ("Like a tank" as somebody upthread said.)
