I bought a thermos from Starbucks when I was with my parents. Nice thing, got it on clearance, so presumably they are no longer using this design. But it's 100% spill proof when the drinking hole latch is shut (trust me, I've tried purposely to spill it and didn't succeed - just to test it before I tossed it in my bookbag). And I discovered another awesome, but slightly dangerous thing about the design today. It doesn't lose heat. AT ALL. I'm dead serious. Tempted to leave some of that tea in there overnight to see if it cools down at all. But I pulled it out this morning in the middle of my first class, and the sides felt cold. Not cool, not lukewarm, COLD. So I figured it must be cool enough I can drink it. Wrong. I burnt my mouth. So I was cursing myself for that, but at the same time thinking how cool that was. I had to remove both the lid and the stopper to let it cool down, and didn't bother to drink another drop till the class ended. By the end, it was cooled enough to be safe, so I put both caps back on. This was at 10am.
Fast forward to 1. I expect it to have cooled down at least a bit by then. Nope. It's still hot.
Then to the middle of my final class. Still hot. Steaming in fact.
And it's still steaming hot now.
I've had thermal mugs and thermoses before, but never one that worked THIS well. It's definitely worth the money I paid for it. But I do need to remember now that liquids need to be cooled to drinkable temp BEFORE they go in the thermos. Because that was painful.