It's a dust cover. .
"I have a few problems with this. . one this falls out a lot and I keep loosing it. Luckily it usually falls out in my pocket so I can find it. Also the lanyard is not useful as it adds to much sticking off the phone. My biggest issue is that the phone case should already have a dust cover integrated in it. One that keeps it from falling out and two this makes these feel like a nickel and dime add on to have you spend a little more on their products and accessories. I love my rockform case but I do think this should be apart of the case and not a seperate product."