What the temperature on a heat protectant actually means

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Researched. We have not used this one long enough to give you a verdict, and we would rather say so than invent one. What follows is how it works, who it suits, and what it will not do. When we have used it properly, this page carries the verdict and the date.

Tresemmé Thermal Creations Heat Tamer Protective Spray

The number on the front of a heat protectant — 450°F, or 230°C — is not a rating. It is a claim, and nothing in particular defines what it has to mean.

That is worth sitting with, because the number looks like an SPF, and an SPF is a different kind of thing entirely. SPF is a defined test with a published method behind it. A heat protectant has no equivalent. No standard test, no agreed threshold, nobody checking. Two bottles both printing 450 may have arrived at it by very different routes.

So the most that number can mean is this: somebody at the brand tested the product at that temperature and was satisfied with the result. What the test was, nobody outside the company knows. It is not a promise that damage stops at 449 and starts at 451.

What is actually in the bottle

Mostly silicones — dimethicone, cyclomethicone and their relatives — usually with a film-forming polymer, sometimes a hydrolysed protein.

The film does three unglamorous things. It spreads heat, so no single point on the fibre takes all of it. It slows the rate at which water leaves the hair. And it lubricates, so a hot plate slides over the strand instead of dragging on it.

None of that is insulation in the sense people imagine. You are not putting a jacket on your hair. You are changing the rate at which something happens.

The mechanism that matters, which is water

Hair holds water. A meaningful fraction of its weight even when it feels perfectly dry, and a great deal more when it does not.

Heat a wet fibre quickly and the water inside turns to steam faster than it can get out, and it leaves voids behind. Hairdressers call the result bubble hair, and under a microscope that is exactly what it looks like: bubbles running down the middle of the strand where the structure used to be.

This is why an iron clamped onto damp hair does more in one pass than a careful week of anything else.

And it is behind the commonest mistake in the category: spraying a protectant on and clamping straight away. Most sprays are largely water and alcohol. Wet hair plus hot plates is the scenario above, and you have just built it on purpose. Let it dry first. The dry film is the protective part. Wet, it is the problem.

The dryer counts too

Nobody thinks of a hair dryer as a heat tool the way they think of an iron. Held two inches away on maximum it delivers plenty, and it delivers it to hair that is by definition wet — which is the state in which heat does the most.

Rough-drying to about eighty per cent from a sensible distance, then finishing, is worth more than most of the products in this article.

Where the dial should be

Most irons go hotter than most hair needs. The top of the range exists for coarse, resistant hair that will not hold a shape otherwise. It is not a default.

Fine hair, bleached hair, or hair that has been through any chemical service wants the lowest setting that does the job — and the way to find that is to start low and work up, which almost nobody does, because starting at maximum works on the first pass and the bill arrives later.

Heat damage is a function of temperature and time together. People who turn the heat up to save a pass usually lose that trade, because the cost climbs faster than the setting does.

Then there is the tool itself. A cheap iron with a poor thermostat overshoots the number on its own display, and that display is the only information you have. No protectant compensates for that.

Who it suits

Anyone using heat, which is the dull answer and the true one. The alternative to a protectant is not going without one. It is using less heat.

Especially anyone with bleached or highlighted lengths, because that hair has already had its internal structure altered and starts the argument from behind.

What it will not do

• It will not undo anything. Hair is dead. There is no repair mechanism in the fibre, so everything done to it accumulates and stays there until it is cut off. That is the fact the whole category sits on top of and rarely mentions.
• It will not protect a section it never reached. Most people spray the outside, style all of it, and conclude the product does nothing.
• It will not make 230°C sensible on fragile hair. It makes it less bad, which is a real thing to buy and a smaller one than the packaging implies.
• It will not survive being applied yesterday. It washes out, and the protection goes with it.

The one thing that decides whether this works

The dial.

Turn it down twenty or thirty degrees and see whether the result is actually worse. Plenty of people find it is not, and that they had been running hot out of habit because the tool defaulted there once and nobody questioned it. That single change does more than anything on the shelf, and it costs nothing.

The product

It has been on shelves a long time and it is cheap, which matters more than it sounds: the commonest failure in this category is under-application, and people ration a bottle they paid a lot for. This is one you can afford to use properly.

The one people are searching for is the Tresemmé Thermal Creations Heat Tamer Protective Spray.

Tresemmé Thermal Creations Heat Tamer Protective Spray

We do not print prices here, because a price we typed last month is a price that is wrong today.

Written by CatieH, who covers nails and hair here.