Once you realize what this is you will want one of our own. 
I kept wasting styrofoam coffee cups at the office until I had this idea. It will convert a disposable styrofoam coffee cup to one that you can use over and over. Cups just snap in and they insulate as well. Print them in different colors for a party.
This is a good idea worth printing. I'll call it the "SmartCup" because I found that it stops me from trashing the planet. It fits perfectly with a standard hot drink cup and it is surprisingly sturdy. It insulates both drink and hands. I'm reminded to clean it instead of throwing it away.