What the world needs now

Pursuant (yeah, I know) to my previous post about clever inventions, I believe I have hit upon a real money maker.

Someone in the world needs to invent a collapsable travel mug.

Travel mugs are great for transporting coffee to and from places, but they're a pain in the ass to transport back when there's no coffee in them. Collapsable plastic cups exist, so why not a collapsable travel mug?

Some problems:
1. Materials. If stainless steel is out, then perhaps the silicon compound used to make some rubbery oven mitts?
2. Heat retention: How to keep the hot liquid hot?
3. Environmental factor: Better than plastic and styrofoam take out cups, the collapsable travel mug would still take a long time to biodegrade.

Potential market:
The number of people in the world who drink coffee/tea while en route.

If anyone out there in Internet-land cares to take up this idea, all I ask in return for my intellectual property is a 5% stake (gross, not net) and a lifetime supply. Any takers?