Best heat protectant: keep the heat off your color

An unbranded flat iron resting on a folded linen towel beside a glossy lock of copper-brown colored hair in soft daylight

You are about to flat iron or blow dry your hair and you do not want the heat to take your color with it. We read the official page of eight protectants. This is what we would pick for your case.

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What we would buy for everyday use
L'Oréal Paris Elvive Dream Lengths Heat Slayer Pre-Iron Spray
Heat Slayer shares 23 of the 29 ingredients the retailer Ulta publishes for the Redken one, which belongs to the same group, with the first four in the same order. Note the line has two formulas: the one compared is the American, and in Europe the brand sells Dream Long. For everyday drying and ironing at home, a lot of bottle for the money. Upkeep between appointments is not the service: what your colorist picks for your hair does not come off a shelf.
If your colored hair spends time in the sun
ghd Bodyguard Heat Protect Spray for Colored Hair
It is the only one of the eight saying it ran a test for its color claim: twice the protection from UV rays on colored tresses. Note two things: it is a sun figure, not an iron one, and the brand never says what product it measured against or how, so it cannot be checked either.
If you avoid silicones on purpose
Olaplex No.9 Bond Protector Nourishing Hair Serum
It is the only one of the eight stating it carries no silicones or sulfates. Its promise is not to stop the heat, even though it also labels its 232 °C: it says it protects the hair bonds. Two warnings. The results it publishes were measured with its shampoo and conditioner on first. And if you want a film that spreads the iron heat, that is exactly the family it states it avoids.
Skip it if you want a temperature figure
Color Wow Dream Coat Supernatural Spray
Color Wow labels none: it says it has "two levels of heat protection", which is a way of grouping ingredients, not a measurement. It does other things well, but it will not give you the number you came for.

We read all 8 official pages verified on September 13, 2026 we have not tested them, and the commission does not decide what appears here How we do it

This is us: we make Blendsor, the colour formula app for salons. We spend our days reading hair colour technical sheets, so reading labels is the job.

Before you buy

Seven of the eight label practically the same ceiling: 450 °F, and ghd 446 °F, which is the same 230 °C. None says what hair it measured, how many passes it survived, or what counted as "protecting". That figure is the ceiling of your iron, not a measure of how much it shields you. So choose on what each one does declare: what is inside, how it goes on, and what it promises about color. And the part no bottle prints: how much heat your hair can take today. The person who colors it knows that.

Out of eight protectants

Label a temperature 7 products
Say under what conditions they measured it 0 products L'Oréal's Spanish page says its test was instrumental, and stops there

Part of: Hair Colorimetry Basics: Guide for Colorists

What is your case?

The seal says what each brand publishes about color duration. It does not measure whether the product works: a bottle with no figure can be excellent at its own job.

Figure with no method explained

L'Oréal Paris

L'Oréal Paris Elvive Dream Lengths Heat Slayer Pre-Iron Spray

The cheap bottle whose list starts the same way as the $39 one.

450 °F

Right for

Anyone drying or ironing often who would rather not spend much on it.

Not for

Anyone wanting to know how that 450 °F was measured: its page does not say, like almost all of them.
- The Heat Slayer list shares 23 of the 29 ingredients Ulta publishes for the $39 Redken, with the first four in the same order
- An ingredient list does not show pH or proportions, and pH is exactly what the expensive one sells
- The line ships as two different formulas: the European one is Dream Long, the American one Dream Lengths Heat Slayer
- Sulfate-free, paraben-free and dye-free, per its page
- Price on the brand’s site: 7,99 $ / 4,4 oz, EE. UU.
- With silicone
- Drugstore price
See it on Amazon Compare
Figure with no method explained

Redken

Redken Acidic Color Gloss Heat Protection Leave-In Treatment

Its asterisk backs the smoothness, not the temperature, and it is built to run with the rest of its line.

450 °F

Right for

Salon-colored hair, and anyone wanting a product built as part of a four-step routine.

Not for

Anyone wanting a single standalone bottle: its page asks for it inside a four-step routine, and that is where the brand measures what it promises.
- Its asterisk is not on the temperature: it backs the "13x smoother" versus a non-conditioning shampoo
- Its page says to use it "as a complete system", with three more products from the line
- The brand highlights vitamin E, arginine, serine, glutamic acid, soybean oil and xylose
- It is a brand from L'Oréal's professional division, the same one as Kérastase
- Price on the brand’s site: 39 $ / 200 ml, EE. UU.
- With silicone
- Salon price
See it on Amazon Compare
Figure with no method explained

ghd

ghd Bodyguard Heat Protect Spray for Colored Hair

The only one saying it tested its color claim, though it never says what it measured against.

2x, against UV rays

Right for

Colored hair that spends time in the sun, and anyone wanting a figure that comes with its test.

Not for

Anyone after a heat figure: that test measures sun, not irons, and the two are not the same thing.
- Its list carries ethylhexyl methoxycinnamate, a sun filter, which fits what it promises
- It labels 446 °F, the same 230 °C as almost everyone else
- The standard version of the same range labels no temperature in the US or in Spain
- It says it ran a technical test on colored tresses against "the market leading product", without saying which one or how it measured
Search for it (no product page) Compare
Figure with no method explained

Olaplex

Olaplex No.9 Bond Protector Nourishing Hair Serum

It labels its 232 °C like the rest, but its core promise runs inside the fiber.

450 °F / 232 °C

Measured with the full routine, not with this bottle alone

Right for

Bleached or breaking hair, and anyone avoiding silicones on purpose.

Not for

Anyone wanting a film that coats the hair: that is exactly the ingredient family it states it avoids.
- It states it carries no sulfates, silicones, phthalates, parabens or protein
- It goes on clean, damp hair, before styling
- Its color claim comes with no written condition behind it
- Leave-in time: On damp hair, before the tool
- Silicone-free
- Salon price
See it on Amazon Compare
Figure with no method explained

Kérastase

Kérastase Chroma Absolu Chroma Thermique Heat Protecting Serum

Its visible figure measures smoothness, not heat or color.

450 °F

Right for

Colored hair that gets blow dried, and anyone wanting a serum that spreads well from mid lengths to ends.

Not for

Anyone comparing temperatures across markets: its European page gives none.
- The asterisk on its "96% smoother" compares with untreated hair, and does not go with the temperature
- It carries vitamin E and lactic acid, which the brand presents as a trap for dulling minerals
- It goes on towel-dried hair, 6 to 10 sprays depending on length
- Leave-in time: On towel-dried hair, leave in
- Salon price
See it on Amazon Compare
Figure with no method explained

Moroccanoil

Moroccanoil Perfect Defense Heat Protectant

The only one that does not start with water, and that changes how you use it.

450 °F / 230 °C

Right for

Anyone drying first and ironing after, and anyone who does not want to feel any weight.

Not for

Anyone after something that talks about color: its product page says nothing about it.
- Its list starts with dimethyl ether, the propellant, and alcohol: the other seven start with water
- The brand presents it with argan oil and panthenol as key ingredients
- Its page allows it on damp or dry hair, and with any styling tool
- Salon price
See it on Amazon Compare
Figure with no method explained

TRESemmé

TRESemmé Keratin Smooth Heat Protection Spray

Cheap, and with no color claim on its page.

450 °F (US)

Right for

Anyone blow drying daily who wants something that does not weigh hair down.

Not for

Anyone buying with color in mind: its page never mentions it.
- The line ships with different formulas on each side of the Atlantic, under different product codes
- Its label changes with the market: 450 °F on the US page and 230 °C on the Spanish one, which is a different product code
- It goes on towel-dried hair, before the dryer or the iron
- Drugstore price
See it on Amazon Compare
Promises care, not a figure

Color Wow

Color Wow Dream Coat Supernatural Spray

The only one that labels no temperature, and says so in other words.

What it does measure: How many washes the effect lasts: three to four

Right for

Thick or frizzy hair blow dried with tension, which is how it asks to be used.

Not for

Anyone comparing by temperature: there is no number to compare here.
- Its "two levels" are a way of grouping ingredients, not a measurement
- It must go on wet hair and is activated by the heat of the dryer
- It states it contains no formaldehyde or formaldehyde-releasing ingredients, and no sulfates
- Leave-in time: On wet hair, activated by the dryer
- Salon price
See it on Amazon Compare

Compare the ones you care about

Tick two or three and they will show up here, side by side.

Product	Label	Figure	How it measured it	In one line
L'Oréal Paris Elvive Dream Lengths Heat Slayer Pre-Iron Spray	Figure with no method explained	450 °F	—	The cheap bottle whose list starts the same way as the $39 one.	See it on Amazon
Redken Acidic Color Gloss Heat Protection Leave-In Treatment	Figure with no method explained	450 °F	—	Its asterisk backs the smoothness, not the temperature, and it is built to run with the rest of its line.	See it on Amazon
ghd Bodyguard Heat Protect Spray for Colored Hair	Figure with no method explained	2x, against UV rays	—	The only one saying it tested its color claim, though it never says what it measured against.	Search for it (no product page)
Olaplex No.9 Bond Protector Nourishing Hair Serum	Figure with no method explained	450 °F / 232 °C	—	It labels its 232 °C like the rest, but its core promise runs inside the fiber.	See it on Amazon
Kérastase Chroma Absolu Chroma Thermique Heat Protecting Serum	Figure with no method explained	450 °F	—	Its visible figure measures smoothness, not heat or color.	See it on Amazon
Moroccanoil Perfect Defense Heat Protectant	Figure with no method explained	450 °F / 230 °C	—	The only one that does not start with water, and that changes how you use it.	See it on Amazon
TRESemmé Keratin Smooth Heat Protection Spray	Figure with no method explained	450 °F (US)	—	Cheap, and with no color claim on its page.	See it on Amazon
Color Wow Dream Coat Supernatural Spray	Promises care, not a figure	—	—	The only one that labels no temperature, and says so in other words.	See it on Amazon

Does a heat protectant actually do anything?

It does, and it helps to know what. A protectant does not put a shield between the iron and your hair. What is measured is a result, not a mechanism: hair pre-treated with certain polymers breaks less after ironing.

And it helps to know who measured it. That work is signed by a polymer manufacturer, not an independent lab: breakage drops noticeably. Drops, not disappears. No brand on this list publishes a study like that for the bottle it sells, and the one that exists is not impartial either.

And one thing matters more than which brand you pick: damage starts sooner the higher the temperature goes. In a study using a curling iron, turning the heat up barely improved curl hold, but the onset of damage was strongly temperature dependent. Translated: before you change bottles, turn your iron down. With one warning, because the gain is easy to lose: do not make up for it with more passes. And if your hair comes from bleaching or highlights, that temperature is set by the person who colors it, looking at your hair, not by a label.

What the asterisk does not back

Less than it looks. Seven of these eight brands print the same ceiling, and not one says what hair it tested, how many passes it survived, or what counted as protecting.

That figure is the ceiling of an ordinary flat iron. It is a compatibility label, the “works up to here” kind, not the result of a measurement.

The asterisk is what gives it away. When there is one near the number, it almost never backs that number:

On Kérastase, the asterisk belongs to the “96% smoother”, compared with untreated hair.
On Redken, to the “13x smoother”, versus a non-conditioning shampoo.
On ghd for coloured hair, to the protection from UV rays.

Only one brand says even what kind of test it ran, and it stops at calling it instrumental. None states the conditions.

So do not shop on temperature: it is the same on almost all of them. Shop on what each one does declare, which is what this page puts in front of you.

The $39 one and the $7.99 one start the same way

This is what came out of putting all eight ingredient lists in one table.

The expensive Redken protectant and L’Oréal’s Heat Slayer share 23 of the 29 ingredients the retailer Ulta publishes for the first. The list compared is the American formula, Dream Lengths Heat Slayer; in Europe L’Oréal sells a different one under the Dream Long name. The first four run in the same order. And the actives Redken highlights on its own site (xylose, arginine, serine, glutamic acid) are in the other list too.

Both brands belong to the same house: Redken sits in L’Oréal’s professional products division, same as Kérastase.

Now, what that does NOT mean, and it matters:

They are not the same formula. An ingredient list runs in order of concentration only above one percent. It never says how much of anything is in there.
It says nothing about pH, which is exactly what the expensive one sells: the word acidic is in its name.
The list of 29 comes from a retailer, not from the brand. Redken’s own site does not publish it openly.

What you can do with the finding: pay the difference knowing what it buys you.

A woman blow-drying her own colored hair at home with a round brush, the dryer held well away from her head

Keep the dryer far and keep it moving: that is the part of heat protection that costs nothing.

Every page asks for something different

Its own page tells you, and they do not all say the same. Some ask for damp hair, some for towel-dried, and one takes it either damp or dry.

But there is a finding from outside the brands that helps you decide. At the University of Manchester they ironed hair treated with a water-based spray and with an alcohol-based one. Chemical damage dropped the same with both. Structural damage was worse when the hair was wet, and the likely cause is water flashing off all at once.

It does not let anyone say one product protects more than another: they tested two laboratory sprays, not bottles off a shelf. What does carry over applies to any of them: there has to be a drying step between the product and the iron. The protectant goes on where its page says, usually damp or towel-dried. Then the hair is dried all the way. And only then does the iron come in.

And watch out, because there is a contradiction between markets here. The American page of Heat Slayer, the one we recommend above, says to apply on damp hair and flat iron straight away. The European page of its sibling Dream Long says dry or slightly damp. Follow the page of the bottle you are actually holding, and keep the drying step in between.

What is actually measured about dye

This is where precision matters, because it is the question that brings most people here.

What is measured is that heat changes the color of the hair itself:

A plate at 172 °C darkened virgin hair in two minutes.
A thermal treatment at 81 °C yellowed grey hair, on both types tested.
Across repeated washing and drying, the color of undyed hair shifted mostly towards lighter.

What we did not find is a study measuring that irons or dryers fade oxidative dye. We looked on PubMed and did not find it. So we do not claim it, however often it gets repeated.

One detail from the same work that surprises: blow drying at a distance and on the move did less damage than letting hair air dry. The dryer is not the problem; the dryer held close and still is.

What this page is not

We have not tested these products. We have no lab and no test panel, and faking a test we did not run would be worse than saying so.

What we did do is read the eight official pages and put them in one table. Reading one label is no achievement; reading eight at once shows what no brand writes on its own: that the figure nearly all of them print is the same one, and that the expensive list and the cheap list start identically.

And it is worth saying what a bottle does not do. A heat protectant does not replace your colorist’s judgement on what your hair can take. If you are coming off a recent lightening service, that conversation is worth more than any of these eight.

What people ask

What is the best heat protectant for colored hair?

If you want a color claim with a test behind it, ghd Bodyguard for coloured hair is the only one of the eight that brings one: twice the protection from UV rays, measured on colored tresses. Note that figure is about sun, not irons. Redken Acidic Color Gloss and Kérastase Chroma Thermique also talk about color, but with no figure behind it.

What does it mean when a protectant says 450 °F or 230 °C?

It means the brand is labelling the ceiling temperature of an ordinary flat iron, not that it measured how much it shields you. Seven of the eight print that same figure and none says what hair it tested, how many passes it survived or what counted as protecting. It is a compatibility label more than a result.

Is the expensive heat protectant worth it?

It depends what the difference buys you. The $39 Redken and the $7.99 L'Oréal share 23 of the 29 ingredients published by the retailer Ulta, with the first four in the same order. That does not make them the same: a list shows neither pH nor proportions, and pH is exactly what the expensive one sells. That is how you decide what the difference buys. And a bottle, at any price, does not do the work of the person who colors your hair.

Do you apply heat protectant on wet or dry hair?

Its own page tells you, and they do not all say the same. Olaplex and Color Wow ask for damp hair. Kérastase and TRESemmé, towel-dried. Moroccanoil puts the dryer in between. One thing that helps you decide: ironing wet hair measures more structural damage than ironing it dry, so the iron goes on hair that is already dry.

Is there a silicone-free heat protectant?

Of the eight, Olaplex No.9 is the one stating it carries none, listed alongside sulfates, phthalates, parabens and protein. Its promise runs elsewhere: instead of coating the hair with a film, it says it repairs the internal bond. If you avoid silicones on purpose, that is the one that fits.

Does flat iron heat fade hair dye?

What is measured is that heat changes the color of the hair itself: a plate at 172 °C darkened virgin hair in two minutes, and a treatment at 81 °C yellowed grey hair. We did not find a study measuring that irons or dryers fade oxidative dye, so we do not claim it. What we do know: damage starts sooner the higher the temperature goes.

Sources and method

Every figure on this page comes from the brand’s official page. This is what each one says, in its own words and in the language it publishes them in, and the day we read it.