Hot water freezing faster in an ice cube tray is commonly reported, a bunch of reasons could explain it. Evaporation can reduce the volume of water, and the sm

Hot water freezing faster in an ice cube tray is commonly reported, a bunch of reasons could explain it. Evaporation can reduce the volume of water, and the smaller volume freezes faster. A hot tray will settle into any ice build up in the freezer (which is common) increasing the rate of heat exchange. Hot water will create currents in the air and water (driven by the higher water temperature) which help the exchange. On the flip side lower temperature differences will often cause a stagnant layer that will reduce the temp exchange, much like sitting in a cold pool which gets better if you want a few seconds... until you move again. The reported experiment reduces the variables by using glass instead of water, so there's no internal flow, but that doesn't stop the airflows generated in the air.