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Side by side

CHI 44 Iron Guard Thermal Protection Spray vs K18 Leave-In Molecular Repair Hair Mask

88% function match · 8 of the 10 functions we compared match Formula overlap 14%. CHI 44 Iron Guard Thermal Protection Spray and K18 Leave-In Molecular Repair Hair Mask share 1 ingredient among each other's most prominent.

These sit in different steps of a routine — CHI 44 Iron Guard Thermal Protection Spray is a heat protectant and K18 Leave-In Molecular Repair Hair Mask is a leave-in. Comparing their formulas is fair; treating one as a replacement for the other is not.

Based on your consultation

Which of these fits your hair?

We check your pattern, moisture need, scalp, fragrance tolerance, weight sensitivity and more against each formula — and say which one lines up.

Your profile at a glance

  • Your answers appear here
  • Your answers appear here
  • Your answers appear here
  • Your answers appear here

When each one is the right call

What each formula is built for, from its own ingredient list.

  • 44 Iron Guard Thermal Protection Spray — heat styling
  • Leave-In Molecular Repair Hair Mask — protein-hungry hair

Side by side

Every trait, aligned

One row per trait, read from each product’s own ingredient list and record. A dash means we have not researched that field for that product — it is not a “no”.

Trait
CHI 44 Iron Guard Thermal Protection Spray — 8 oz container CHI

44 Iron Guard Thermal Protection Spray

  • Heat protectant
  • Salon
  • Sulfate-free
  • Silicone-free
K18 Leave-In Molecular Repair Hair Mask — 1.69 oz container K18

Leave-In Molecular Repair Hair Mask

  • Leave-in
  • Prestige
  • Sulfate-free
  • Silicone-free
Price, size & price per ounce
$15–18 8 oz · $2.09/oz
$0.01 1.7 oz · $0.01/oz

Compared at different sizes — 8 oz against 1.7 oz. Per-ounce prices favour the larger bottle.

Value / price positioning
Priced with its peers $$$$$ Salon tier · costs less than 55% of the 564 heat protectants we’ve priced
Lower cost than most leave-ins $$$$$ Prestige tier · costs less than 100% of the 491 leave-ins we’ve priced
Best for hair types
Straight–Curly Smoothing and thermal products span straight through curly hair. Your hair
All types Nothing in the formula or the claims narrows this to one pattern. Your hair
Moisture level Same
High Humectants near the top — water-binding is a headline mechanism here. Your hair
High Humectants near the top — water-binding is a headline mechanism here. Your hair
Heat protection
High The brand states a protection temperature — a label claim, not a measurement. Your hair
—
Slip / detangling Same
High Conditioning agents sit high in the list — this is a detangling formula. Your hair
High Conditioning agents sit high in the list — this is a detangling formula. Your hair
Weight on hair Differs
Light Water-first and light: unlikely to flatten fine hair. Your hair
Medium Middle of the range — noticeable on fine hair, light on coarse hair. Your hair
Fragrance
Present Fragrance is listed; it sits below the working ingredients. Your hair
Present Fragrance is listed; it sits below the working ingredients. Your hair
Protein Same
Prominent Protein high in the list — a strengthening formula, not a moisture one. Your hair
Prominent Protein high in the list — a strengthening formula, not a moisture one. Your hair
Silicone / wax buildup Same
None Nothing here needs a detergent wash to remove. Your hair
None Nothing here needs a detergent wash to remove. Your hair
Clarifying wash needed
Low Your hair
Low Your hair
Oils and butters Same
—
None No oils or butters in the list. Your hair
Fast-drying alcohol Same
High in the list Fast-drying alcohol in the first three ingredients. Your hair
—
Formula completeness
out of 10
Complete for its job
out of 10
Complete for its job
Who should choose this
  • Heat stylingthe brand states protection to 450°F
  • Protein-hungry hairthat stretches and stays stretched when wet
  • Maximum slipfor hair that tangles the moment it is wet
  • Fine hairthat flattens under most products
  • Protein-hungry hairthat stretches and stays stretched when wet
  • Maximum slipfor hair that tangles the moment it is wet
  • Dry, thirsty hairhumectants and emollients both sit up front
  • Curly-method routinesno sulfates and no water-insoluble silicones
Why you might skip it
  • Scents bother youthis product carries a scent
  • Protein-sensitive hairthat goes stiff or straw-like on protein
  • Very dry or damaged hairit contains fast-drying alcohol
  • Scents bother youthis product carries a scent
  • Protein-sensitive hairthat goes stiff or straw-like on protein
  • Very dry or damaged hairit contains fast-drying alcohol
from the formula stated by the brand reported by reviewers Scale: 1 dot low · 5 dots high, within this product type.
More facts about each one
Type
Heat protectantspray
Leave-incream
Where to buy
Brand website · Target
Salons · Sephora · Ulta
Free of
  • sulfate-free
  • silicone-free
  • curly-method compatible
  • sulfate-free
  • silicone-free
  • curly-method compatible
Vegan
Not vegan · ingredient list
—
Cruelty-free
—
Cruelty-free · brand states
Scent
Scented, not described
Scented, not described
Heat protection
up to 450°F
—

Facts as we recorded them. A dash means we have not researched that field for that product — it is not a "no".

The bottom line

The bottom line depends on your hair

Which of these two suits you is a question about your hair, not about them. The consultation answers it — and tells you what your routine needs around it.

Take the consultation

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The detail behind the table

Where the readings above come from: the ingredient lists themselves, each brand’s claims checked against them, what owners report, and cost per ounce in context.

Shared and distinct ingredients

Shared and distinct ingredients

Computed from the ingredient lists as printed. "Shared" means both lists carry it; where it sits on each label is stated, because position is what tells you how much.

What both formulas carry

Ingredient44 Iron Guard Thermal Protection SprayLeave-In Molecular Repair Hair Mask
Water
Neutral
#1Leading
#1Leading
Alcohol Denat.
Drying
#3Leading
#2Leading
Polysorbate 20
Stabilizes
#4Supporting
#8Supporting
Fragrance
Fragrance
#16Below the 1% line
#17Below the 1% line
Hexyl Cinnamal
Fragrance
#19Below the 1% line
#20Below the 1% line

What only one of them carries

44 Iron Guard Thermal Protection Spray

Leave-In Molecular Repair Hair Mask

Full ingredient list — 44 Iron Guard Thermal Protection Spray (20)
Full ingredient list — Leave-In Molecular Repair Hair Mask (23)

Claims check

What each brand says, against what each formula shows

Claims are quoted from each brand. We only mark one supported, partly supported, or conflicting when that product’s ingredient list actually speaks to it.

Verdicts44 Iron Guard Thermal Protection SprayLeave-In Molecular Repair Hair Mask
Supported
0
1
Partly supported
2
0
Stated by brand
2
3
Potential conflict
0
0

44 Iron Guard Thermal Protection Spray

  • Superior heat protection from the inside out against styling and finishing damagesPartly supportedSold for hot tools; untestable here.
  • Protects Hair from Thermal ToolsStated by brandCan’t be confirmed from label.
  • Designed to withstand temperatures up to 450FPartly supportedSold for hot tools; untestable here.
  • Will not clump or build up resulting in no flakesStated by brandCan’t be confirmed from label.

Leave-In Molecular Repair Hair Mask

  • 4-minute leave-in treatment to reverse hair damageStated by brandCan’t be confirmed from label.
  • Works on the molecular level to reverse hair damage in just 4 minutesStated by brandCan’t be confirmed from label.
  • Repairs damage from bleach + color, chemical services, and heatSupportedReinforces a damaged strand.
  • Works on all hair typesStated by brandSee the fit panel instead.

What owners say

What people report

Recurring themes our researchers wrote in their own words from sourced reviews. We do not store or scrape star ratings, and we never balance one product’s themes against another’s by inventing them.

CHI 44 Iron Guard Thermal Protection Spray draws complaints about dryness and weight.

44 Iron Guard Thermal Protection Spray

Helps tame wavy, frizz-prone hair

Praised for scent as a good first CHI product for thick hair

Sprays on sticky/heavy like a protecting wax, leaves hair tacky and dry after heat styling

Leave-In Molecular Repair Hair Mask

Strongest praise from users with visibly damaged/over-bleached hair; more modest impact reported on already-healthy hair

chemically damaged hair

Scent described as subtle/faintly medicinal rather than typical perfumed haircare scent

Price-to-value repeatedly flagged as expensive for the bottle size, though many conclude it is worth it for damaged hair

Mixed on weight -- lightweight for most, but over-applying causes heaviness per a subset of reviewers

Price check

Cost per ounce, in context

Cost per ounce against every product of this type we have priced, each at the size it is most often sold in. Value labels are computed from that percentile and from how many products that do the same job cost less; they are comparisons, not judgements about a brand.

$0.01/oz vs $2.09/oz — CHI 44 Iron Guard Thermal Protection Spray costs about 209× more per ounce than K18 Leave-In Molecular Repair Hair Mask.

44 Iron Guard Thermal Protection Spray

Against 564 heat protectants with a computable unit price.

Leave-In Molecular Repair Hair Mask

Against 491 leave-ins with a computable unit price.

Value read44 Iron Guard Thermal Protection SprayLeave-In Molecular Repair Hair Mask
Label
Priced with its peersSits in the middle of the range for heat protectants per ounce.
Lower cost than most leave-insCosts less per ounce than most leave-ins we have researched.

Computed from cost per ounce against every product of this type we have priced, and from how many products that do the same job cost less. It is a comparison, not a judgement about the brand.

Compare with something else

Close formulas to each of these, as their own comparison pages.

44 Iron Guard Thermal Protection Spray vs 44 Iron Guard Botanical BlissCHI · 93% function matchLeave-In Molecular Repair Hair Mask vs 44 Iron Guard Botanical BlissCHI · 81% function match44 Iron Guard Thermal Protection Spray vs Honey Combout Moisturizing DetanglerCurlyKids · 88% function matchLeave-In Molecular Repair Hair Mask vs Curl SealerTaliah Waajid · 75% function match44 Iron Guard Thermal Protection Spray vs This Is A PrimerDavines · 81% function matchLeave-In Molecular Repair Hair Mask vs Honey Combout Moisturizing DetanglerCurlyKids · 75% function match44 Iron Guard Thermal Protection Spray vs 2% Squalane Anti-Frizz Leave In ConditionerAct+Acre · 79% function matchLeave-In Molecular Repair Hair Mask vs Leave-In Conditioner, Fragrance FreeSEEN · 74% function match

44 Iron Guard Thermal Protection Spray · Leave-In Molecular Repair Hair Mask · All heat protectants in the library

How this page was made

  • This page is assembled from the same researched records the individual product pages render: identity, each ingredient list as printed, each brand's own claims, dated price observations, and review themes written in our researchers' own words. Nothing on it is written per comparison.
  • We do not rank these against each other. Which of them suits you depends on your hair, and that is what the consultation works out.
  • The formula similarity percentage is a stored, precomputed number: position-weighted overlap of the two ingredient lists blended with agreement on the attributes we derive. It measures how alike two formulas are, not how well either works.
  • The value band is a fixed label over two stored numbers: this product’s cost per ounce as a percentile of every product of this type we have priced, each at the size it is most often sold in, and how many products we score as doing the same job cost at least a quarter less per ounce.
  • The "Is this right for you?" panel reads only your own consultation answers, and it applies exactly the filters our recommendation engine applies. It is computed when you load the page and is never stored on it.
  • 8 sources were consulted across the products on this page.
  • Ingredient order tells you relative amount only above roughly 1%. Prices are observations on the dates shown and change without notice. We do not sell these products and take no placement fees.
  • This is cosmetic information, not medical advice, and nothing here diagnoses or treats a health condition.

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