> to people saying the cap is the weak point: 9/10 times it's the bottom that gives in first. It may be the case for a typical water bottle but thermoses have

> to people saying the cap is the weak point: 9/10 times it's the bottom that gives in first. It may be the case for a typical water bottle but thermoses have much larger caps. The maximal force that a cap can hold is proportional to its perimeter (~r), the force itself is proportional to the area of the cap (~r^2) and the pressure. So larger caps can blow off by lower pressure. I would bet that for a thermos the weak point is the cap.