iPhone 4s Bumper for flexPLA

We recently recieved our first batch of flex EcoPLA filament from http://www.formfutura.com (this is not intended as a blunt form of advertisement).
The qualities of this very interesting materials inspired me to make a bumper for the iPhone that can only be used if printed with flex PLA, but then fits really tight, like a real bumper.
The perimeter of the bumper has two recessed areas that make it easier to find the volume buttons and the power button without looking.
Beware: this Bumper is probably useless if not printed with flexible PLA!
[Edit] I uploaded an improved version that sits a little bit tighter on the phone.
[Edit] I upoaded the latest version (v7) of the bumper, both as STL and as a sketchup file. I closed the holes for the volume and on/off buttons, like it is on many other bumpers. itôs still work in progress, but feel free to improve and share (it's alreasy carrying a CC-license!)