A fairly standard size and shape that is consistent across most brands. If you live in Europe, however, you are most likely doing your shopping at the easiest and cheapest place: Ikea. Unfortunately, Ikea rocks a different style, so your cup can look like any one of these:
And the cup you use at home could be vastly different from the cup you use at work. So I thought why not make a cozy that could cover a multitude of sizes and shapes. Thus the convertible coffee cup cozy.
If your cup is large, you can just use the top button, if its smaller or curvaceous (think the middle Ikea cup), use the middle buttons as well for a tighter fit. If your cup at work is shorter than your cup at home (think the first Ikea cup), just fold it down, button it underneath, and you're all set!
I will be making cozies for the "American" coffee cup as well and these are available in any color you can think of in my store, just ask!