Glass. I bought it off eBay international. Samsung in USA won't cover the warranty because I bought it overseas. I emailed the seller to see if he will exchange it, but it'll cost me at least $50 to send it back . I'm unsure what to do as a brand new device should be free of imperfections and it's right on the glass. It arrived factory sealed and doesn't look like a shipping issue as it seems to be under the first layer. It's not super noticeable when device is on but under the right angle I can definitely notice it. 
