Scope. This page provides a controlled reader-run protocol and does not claim site-run measurements. For cooking, cooling, storage and reheating, follow the current official guidance linked on the page.
A heat diffuser is a flat plate that sits between the hob and the pan. The claim is that it lowers the temperature the pan can be held at and makes that temperature steadier. It costs very little, it is recommended constantly in gentle-cooking contexts, and as far as we can find nobody has published a measurement of either claim.
That is a small enough question to answer properly, and it has an obvious control that reviews of the object almost never run: the things you already own that might do the same job for nothing.
Before anything else: induction
If you cook on induction, this question is probably already settled, and it is worth saying so at the top rather than burying it.
An induction hob does not heat the pan by contact. It induces a current in a ferrous pan base, and the pan itself becomes the heat source. Put a plate between the hob and the pan and one of two things happens. If the plate is not ferrous, the hob has nothing to couple with and most hobs will simply refuse to run, reporting no pan detected. If the plate is ferrous, then the plate becomes the heated object and the pan on top of it is being warmed by contact with the plate, which is a different arrangement from the one the hob was designed around and which changes the behaviour of the hob's own control loop.
Some plates are sold as induction-compatible and are intended for that second arrangement. Whether it measurably improves anything is what the test below checks, and there is a real possibility that the answer on induction is no.
For a lot of readers that closes the buying question without requiring a product result. Induction's low-heat problem has a different cause and different fixes, covered in how to hold a pan at 60°C on equipment that does not want to.
What a diffuser claims to do
Two claims, which are separable and worth testing separately.
Claim one: a lower floor. That the lowest stable pan temperature achievable with the diffuser in place is lower than the lowest stable pan temperature without it. This is the claim that matters to anyone whose hob will not go low enough for gentle work.
Claim two: greater stability. That the pan temperature fluctuates less over time with the diffuser in place. This matters most on hobs that deliver low power by cycling full power on and off, where the pan is not sitting at a low temperature so much as repeatedly visiting one.
An object could satisfy one claim without the other. A plate could lower the floor by wasting energy sideways while doing nothing for stability, or smooth the cycling without changing the floor at all.
The test
The same protocol runs for every configuration, on every hob type you have available, with nothing changed between runs except the thing being tested.
| Step | What is done | What is recorded |
|---|---|---|
| 1 | Pan on hob at the lowest setting that holds, contents stated and identical every run | Time to stabilise |
| 2 | Hold for a stated period once stable | The full logged temperature trace |
| 3 | From the trace, extract the floor | Lowest stable held temperature |
| 4 | From the same trace, extract the stability | Peak-to-trough swing, and the cycle period if the hob cycles |
| 5 | Repeat a stated number of times per configuration | Every run kept, not an average |
Controlled and stated for every run: the pan, its base thickness and mass, the contents and their mass, ambient temperature, the hob and its setting, and whether a lid was fitted. The pan and the contents do not change between configurations. The two outputs are the floor and the swing, and both must be measured on your own setup.
The configurations, including the free ones
This is the part that makes the test worth running. The diffuser is not compared against nothing. It is compared against the alternatives a reader already owns, measured identically.
- Bare hob. The control.
- The purchased diffuser. How it was obtained (purchased, gifted or loaned) stated on the results row.
- An empty heavy pan used as the diffuser. A cast-iron or other heavy pan placed directly on the hob with the cooking pot standing on it. Free, if you own one.
- A water bath on the hob. The cooking pot standing in a larger pan of water. This caps the temperature the contents can reach by a completely different mechanism, and it is free.
- A folded cloth in the base of an oven water bath. Not a hob configuration. A folded tea towel or a fold of paper in the bottom of a roasting tin, under the vessel, in an oven water bath. It is the traditional answer to a custard sitting directly on a hot metal base, and it is included for comparison with the hob configurations rather than against them.
- Simply turning the hob down, plus moving the pan off-centre. The zero-object option, which deserves a measured row because it is what most people do and nobody has checked whether it is enough.
A safety line that has to be explicit: a cloth never goes on a hob. Configuration 5 is an oven water bath only, with the cloth submerged under water in the tin. Anyone who reads "a folded towel works as a diffuser" and puts one on a gas ring or a radiant plate has read a sentence we did not write.
Which hob types benefit, and which do not
The result is expected to depend heavily on hob type, so record results per hob and never average them across hobs.
- Gas. A flame is a concentrated, uneven heat source, and the plausible mechanism for a diffuser is spreading it. If the object works anywhere, this is where.
- Radiant electric. These hold heat in the element and keep delivering it after the dial moves, so the plausible benefit is smoothing rather than lowering.
- Induction. See above. Mostly the question does not arise.
The verdict, decided in advance
Write the decision rule before running the measurements:
- If the purchased diffuser lowers the floor or reduces the swing by more than the run-to-run variation of your own method, and the free alternatives do not, it has earned its place; note what it did.
- If a free alternative measures the same, use the free one. No purchase, regardless of how little the object costs.
- If nothing in the list changes the floor or the swing measurably, the object does nothing worth the drawer space, and the answer is to buy nothing.
- If the effect exists but is smaller than the difference between two settings on your own hob, it is a judgement call whether it is worth owning.
The last outcome is the one we consider most likely, and it is worth naming in advance so that a modest measured effect does not get written up as a discovery.
In Plain English
A heat diffuser is a plate that goes between hob and pan, claimed to let you hold a lower and steadier temperature. Test both claims against the free alternatives with the same protocol and change only the interface between hob and pan.
If you cook on induction, the question mostly does not apply to you: the hob heats the pan directly, and putting a plate in between either stops it working or turns it into a different arrangement altogether.
This helps you if your hob will not go low enough for gentle work and you are considering spending money on it. The moment to use it is before that purchase. What to do next is to try the free version first: put an empty heavy pan on the hob, stand the cooking pot on top, and see whether the problem goes away. If it does, you have your answer and you have spent nothing.
Where to go next
This page is a reader-run protocol, not a site result. Keep every configuration's raw trace with the recorded hob, pan, load, and diffuser so the comparison remains auditable.
For the free approaches to the low-heat problem, read how to hold a pan at 60°C on equipment that does not want to. If you are working out what to acquire and in what order, what to buy first puts this object a long way down the list.
Related technique: Twelve Ingredients Worth Paying More For, And Eight That Aren't.