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Leave-In Molecular Repair Hair Mask 5mL
4.7
Rated 4.7 out of 5 stars
8,452 Reviews

leave-in molecular repair hair mask

4-minute leave-in treatment to reverse hair damage
OR

Every purchase supports K18 x Plastic Bank efforts to radically simplify waste.

In 2022 we stopped 147 Metric tons of plastic
=
7.3M+ single-use plastic bottles from reaching the ocean

Description

A leave-in treatment mask for all hair types that clinically reverses damage in 4 minutes. The patented peptide technology works to repair damage from bleach, color, chemical services & heat – restoring strength, softness, smoothness, and bounce to hair.

Repairs Damage Caused By

  • Bleach + Color
  • Heat
  • Chemical Services

IN the shower

  1. Shampoo, do not condition.

OUT of the shower

  1. Towel dry thoroughly.
  2. Begin with 1 pump of the K18 Mask and add more as needed depending on the length, thickness, and condition.
  3. Work evenly into hair from ends to roots, one pump at a time.
  4. Let sit for 4 minutes to activate.
  5. Do NOT rinse out.
  6. Style as usual.

creates hair like new

Traveling deeper into the inner layers of hair than traditional repair products, our revolutionary patented K18Peptide™ is just the right size and makeup to fit in and reconnect broken keratin chains, renewing hair with strength, softness, smoothness, and bounce. You can feel and see the difference with the first use.

Start by using K18 after the first 4-6 washes. Then switch to maintenance mode for a boost of renewed strength, softness, smoothness, and bounce when needed.

  • DO use a clarifying shampoo if you’re a heavy product or dry shampoo user to remove buildup and help our peptide penetrate and get where it needs to go.
  • DO wait the full 4 minutes before styling or applying other product
  • DO use every 4-6 shampoos consecutively to see and feel ongoing results
  • DON’T condition your hair before application (trust us, most won’t need it after K18, if you still need, add a leave-in after the 4-minute window is up post-application)
  • DON’T overuse, a little goes a long way.
  • DON’T rinse out. This is a leave-in, so you know, leave it in!

Our K18Peptide™ is clinically proven to reverse damage in just 4 minutes.

  • Heals damage from bleach, color, chemical services, and heat
  • Restores strength, softness, smoothness, and bounce
  • Doesn’t wash away with shampoo, leaving lasting results
  • Vegan, color-safe, cruelty-free

up to 91% original strength*
up to 94% original elasticity*

* Results observed in a clinical study while using mist and mask as part of a bleaching treatment. Results may vary depending on hair type, quality and history.

Water (Aqua) (Eau), Alcohol Denat., Propylene Glycol, Cetearyl Alcohol, Dicaprylyl Ether, Cetyl Esters, Behentrimonium Chloride, Polysorbate 20,sh-Oligopeptide-78 (K18Peptide™), Hydrolyzed Wheat Protein, Hydrolyzed Wheat Starch, Isopropyl Alcohol, Tocopherol, Phenoxyethanol, Potassium Sorbate, Citric Acid, Fragrance (Parfum), Geraniol, Linalool, Hexyl Cinnamal, Benzyl Alcohol.

Description

A leave-in treatment mask for all hair types that clinically reverses damage in 4 minutes. The patented peptide technology works to repair damage from bleach, color, chemical services & heat – restoring strength, softness, smoothness, and bounce to hair.

what you can expect
by damage type

backed by science,
loved by stylists
Our community of stylists and colorists believe K18 is liberating hair—no matter the hair type or generation.
“K18 allows me to go everywhere I want to go with my color work and the end result is my guests get to be bright and shiny and healthy.”

– Christine Thompson, Director of Color at Spoke & Weal
got questions?
Get started here
When hair gets damaged, the polypeptide chains (keratin chains) that make up the inner structure of hair strands become weakened and break. For context, there are billions and billions of polypeptide chains (keratin chains) in a single strand of hair. When these are damaged, hair’s core structure responsible for elasticity and strength becomes compromised and as a result it loses its resiliency and shine—or the look and feel of healthy hair.

After spending a decade in the lab scanning and testing all amino acid sequences across the entire keratin genome that makes up human hair searching for a breakthrough, we discovered one unique sequence (a bioactive peptide) that brings damaged hair back to its original, youthful state. This is our K18Peptide™.

Traveling deeper into the inner layers of hair than traditional repair products, our revolutionary peptide is just the right size and makeup to fit in and reconnect those broken polypeptide chains (keratin chains). And because our peptide is a bit of an overachiever, as a result of this reconnection, any disturbed disulfide bonds are also re-conformed.

Our peptideemploys biomimetics to get the job done. To put it simply: Biomimetics is the practice of learning from and mimicking nature. Mimicking the natural structure of keratin building blocks (amino acid sequences), our K18 bioactive peptide is recognized as natural by the hair. It’s not washed away by water or shampoo like traditional bonding agents either, making K18 a genuine, lasting solution for damaged strands.
Our patented peptide is a unique sequence of amino acids that travels deep into hair’s core structure to fit in and reconnect broken polypeptide chains (keratin chains) responsible for hair strength and elasticity.

An Analogy: When building proteins, the order of the amino acids determines the kind of protein and its properties, much like the way letters are arranged to make meaningful words and sentences. In the same way the order and where each word sits in a sentence leads to its overall meaning, K18 is the magic word that fits right in, integrating itself with the keratin chains as the hair recognizes it as a natural building block.
K18 is most effective on clean, towel-dried hair. Conditioners use silicones and conditioning agents that form heavy coatings on hair , preventing our peptide from reaching the broken polypeptide chains deep inside hair’s inner layer.
We like to keep our formulas minimal, only using the exact amount of ingredients needed to get the peptide where it needs to go. Our unique blend of 3 alcohols function to open up the hair cuticle so the K18Peptide ™ can penetrate the inner most layer of hair, reaching the broken polypeptide chains (keratinchains). Here the alcohol serves as an agent to optimize the hair environment for K18 to work on a deeper level.
You will start to see stronger, softer, healthier hair after just one use.

Renews strength, softness, smoothness, and bounce

K18 strengthens hair’s core structure, restoring damaged curl patterns and leaving strands looking and feeling like new.
K18 reconnects broken keratin chains, restoring hairs elasticity and strength meaning coily hair can be renewed and brought back to its original springy, healthy shape.
K18 restores strength, softness, smoothness, and bounce so even the sleekest hair can feel like new.
4.7
Rated 4.7 out of 5 stars
Based on 8,452 reviews
Reviews Summary
Customers say this leave-in hair mask transforms their hair texture and manageability after just one use. Many reviews mention noticeable improvements in softness and reduced frizz. Users with curly, fine, and color-treated hair report positive results. The mask works well for various hair types, with many noting improved texture and easier styling. While some mention the product's high price point, most find a little goes a long way. A few users recommend using conditioner alongside the mask for best results. Reviews consistently highlight the mask's effectiveness for addressing dry, brittle hair concerns.
8,452 reviews
  • Melanie C.
    Verified Buyer
    Reviewing
    Jumbo Leave-In Molecular Repair Hair Mask 100mL
    I recommend this product
    Age 45 - 54
    Hair Concern Frizz, Split-Ends
    Hair Type Grey Hair, Medium Density, Straight/Wavy
    My Results Less Frizz, Stronger Hair, Less Breakage
    Rated 5 out of 5 stars
    1 week ago
    Fantastic

    My hair has never been longer, I don’t color my hair, I heat style occasionally. I’m 49 with waist length hair. This really helps decrease breakage & increase retention.

    K Profile picture for K18Hair
    K18Hair
    1 week ago

    We're so thrilled to hear that the Jumbo Leave-In Molecular Repair Hair Mask is helping with breakage and retention for your beautiful waist-length hair, Melanie! It's amazing that you've been able to maintain such incredible length, and we're so glad our mask is supporting your hair health journey. Thank you for sharing your fantastic experience with us!

  • Emilly C.
    Verified Buyer
    Reviewing
    Jumbo Leave-In Molecular Repair Hair Mask 100mL
    I recommend this product
    Age 25 - 34
    Hair Concern Heat damage, Frizz, Dryness, Split-Ends
    Hair Type Thick/Coarse, Curly/Coily
    My Results Bouncy Hair, Shinier Hair, Smoother Hair, Less Frizz
    Rated 5 out of 5 stars
    1 week ago
    More gloss and shine to my hair

    I often get blow outs and use heat so my hair gets dull and looks dry. It’s not like my hair was overly damaged, but it looks so glossy and hydrated after using this treatment 2x.

    K Profile picture for K18Hair
    K18Hair
    1 week ago

    Thank you for sharing your experience and for including photos, your hair looks AMAZING! We’re so glad to hear that the treatment is bringing back that glossy, hydrated look, even with regular blowouts and heat styling. We love that you’re already seeing results after just two uses, Emilly!

  • Karen
    Verified Buyer
    Reviewing
    Full-Size Leave-In Molecular Repair Hair Mask 50mL
    I recommend this product
    Age 65+
    Hair Concern Dryness, Extending time between washes
    Hair Type Grey Hair, Curly/Coily
    My Results Less Frizz, Bouncy Hair, Defined Curl/Wave Pattern, Soft Touchable Hair, Visible Difference
    Rated 5 out of 5 stars
    2 weeks ago
    was skeptical but this is pretty amazing

    Honestly, I thought people were suckers for buying so expensive a product. But I kept looking at it. And yes, I forked out $29 for a half ounce to check it out.

    I usually style my hair dripping wet with gels like Innersense I Create Curl Memory, so having to towel dry my hair stumped me for a while. Because without enough water that gel would leave my hair a hot stiff mess. And then not using conditioner? Heresy!

    But I tried it. I can detangle my hair using a moisturizing shampoo so that wasn't a problem. I towel dried my hair - gasp! - and applied 3-4 pumps of the Hair Mask. My hair immediately felt great; I left it in for a few minutes and then combed it through. When I applied gel to my hair, I added water to distribute it equally throughout my hair. That seemed to work. And when my hair was dry it was clear it didn't disrupt the repair mask.

    But it's in the days after application that this mask really began to make a difference. I like to get at least 5 days out of my hairstyle before shampooing or even wetting it again, Hence the gel. After 5 days, The tight curls loosen up and usually get much frizzier. If I want decent hair after a swim, I have to touch it up in some way shape or form. But with the hair mask, MY curls were looser but still formed. My hair felt soft, smooth and hydrated. And there was so much less frizz, I just had to touch up the edges — this after swimming under a silicone swim cap which can wreck a style. So I thought about getting another trial…

    K Profile picture for K18Hair
    K18Hair
    1 week ago

    We're so thrilled to hear about your incredible transformation with the Full-Size Leave-In Molecular Repair Hair Mask, Karen! It's amazing how you went from being skeptical to experiencing such wonderful results - your curls staying formed, soft, and hydrated even after swimming is truly remarkable. Thank you for sharing your detailed experience and showing how the molecular repair really does make a lasting difference in your hair's health and manageability!

  • Danylle W.
    Reviewing
    Jumbo Leave-In Molecular Repair Hair Mask 100mL
    I recommend this product
    Age 35 - 44
    Hair Concern Chemical damage, Split-Ends, Extending time between washes, Frizz, Fragile/brittle hair
    Hair Type Fine/Thin, Straight/Wavy
    My Results Visible Difference, Soft Touchable Hair, Less Frizz, Stronger Hair, Shinier Hair
    Rated 5 out of 5 stars
    2 weeks ago
    I was skeptical but this stuff is a MIRACLE!

    I was recommend this by my hair stylist. I finally swallowed the price tag and bought it and I feel so dumb for not buying this sooner. I went through too many stylists who completely destroyed my hair before finding a good person and my hair needed a ton of TLC. This has brought my mushy overprocessed frizzy hair back to feeling like my virgin hair again. How!?!?! This stuff is magic! Seriously, MAGIC. My dark blonde fine hair was so overprocessed it lost all its natural shine and slight waves. This stuff brought that back in ONE treatment. Every week I can't wait for my k18 Sunday where I use their detox shampoo and put this on after. I keep it in my hair for a few days before washing again. I am in LOVE! THANK YOU!!!!

    K Profile picture for K18Hair
    K18Hair
    2 weeks ago

    It's amazing how the molecular repair technology can transform your hair and restore that natural shine and texture in just one treatment. Thank you for sharing your incredible experience with us!

  • Hope L.
    Verified Buyer
    Reviewing
    K18 x Future Society Limited Edition Scent Mask
    I recommend this product
    Age 35 - 44
    Hair Concern Chemical damage, Heat damage, Fragile/brittle hair, Frizz, Dryness
    Hair Type Fine/Thin
    My Results Cleaner, fresher hair, Shinier Hair, Visible Difference, Less Breakage, Soft Touchable Hair
    Rated 5 out of 5 stars
    2 weeks ago
    Nothing else measures up

    This is by far THE BEST leave in mask I have ever used, I love the long lasting scent it leaves, but the most important part

    I accidentally over processed my roots and other parts of my hair I HAD to save my hair and this product surely did my hair felt amazing after just one use but now just 3 uses later im obsessed my hair is soooo soft, silky smooth and feels brand new i cannot thank this company enough for saving my hair

    Totally worth it

    K Profile picture for K18Hair
    K18Hair
    2 weeks ago

    We're so thrilled to hear that the K18 x Future Society Limited Edition Scent Mask saved your hair, Hope! Thank you for sharing your experience with us!

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