Sometimes, but not reliably in every experiment. The Mpemba effect describes cases where a warmer sample begins to freeze before a cooler one under particular conditions. Evaporation, convection, container shape, freezer contact and supercooling can all affect the result. If two otherwise identical samples cool under ordinary conditions, the initially colder one usually has less heat to lose; claims of a universal hot-water advantage are misleading.
First define ‘freezes faster’
A sample can reach 0°C, form its first ice crystal, or become fully solid at different times. These are not the same endpoint. A hot sample may reach the freezing point later yet form ice first if the two samples supercool by different amounts.
Why experiments can differ
Several factors can change the comparison: evaporation reduces the amount of water, warmer water can circulate differently, containers may make different contact with a freezer shelf, and dissolved gases or impurities can alter ice nucleation. A study questioning the Mpemba effect showed how measurement choices and experimental details can make broad claims misleading. [1]
Other experiments have observed a Mpemba effect under selected conditions, including when nucleation and supercooling are carefully controlled. [2] The result is therefore conditional, not a contradiction of basic heat transfer.
The careful conclusion
Hot water does not have a universal ability to freeze before cold water. Under some defined setups, a warmer sample can begin freezing first because the whole cooling and nucleation process depends on more than starting temperature.
If you want to test it, use identical containers, equal water amounts, the same freezer position and a precise definition of the freezing endpoint. Repeat the experiment: one surprising result is not enough to establish a general law.
Sources and evidence
- Scientific Reports — Questioning the Mpemba effect ↗
Why imprecise claims and uncontrolled conditions complicate the effect.
- Royal Society of Chemistry — Experimental investigation of the Mpemba effect ↗
Recent experiments testing when hot samples can freeze faster.
- American Journal of Physics — When does hot water freeze faster than cold? ↗
Conditions under which the effect may be observed.
Sources consulted: 11 October 2026. Written with AI assistance and checked against the linked references; not independently reviewed by a subject specialist. Sources do not endorse this article. See our editorial policy.
Revision: Original explanatory article prepared from linked scientific and institutional sources; scope and uncertainty are stated in the text.