Water expands when it freezes, in my head thermos is an extremely rigid structure, how do you stop it from rapturing?
But also as the ice freezes I believe it becomes more buoyant and that rigidity causes the ice to be lifted up when it exerts force on the thermos interior.
I've seen some other ideas like freezing water in a camping cooler with its top open.
But then, why aren't my ice-cubes made in the regular fridge tray clear? The same principle should apply: they should be clear at the top, where the tray is open.
In an insulated vessel, the sides and bottom remain liquid until the frozen portion grows down from the top, pushing the cloudy bit to the bottom, which you can then just lop off.
From the post you’re replying to: 2 to 3 inches of water at the bottom … expands to fill the thermos
Air compresses. A lot.