I Tried The K18 Molecular Repair Hair Oil, And It Really Hydrated My Hair

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Written by Annie Walton-Doyle

Updated: March 9, 2024

We purchased the K18 Molecular Repair Hair Oil for our writer to put to the test. Keep reading for our full, hands-on product review.

K18 Oil In Post Image
Annie Walton-Doyle / Timeless Hairstyles

The Bottom Line

For anyone who wants a finishing oil that works as both a styling product and a reparative treatment, the K18 Molecular Repair Hair Oil is an excellent choice. It helps add hydration and smoothness to hair after one use, but the science-y bit also ensures the oil helps treat hair damage over time for a healthier and happier mane.

Even the most basic of haircare routines can see the benefit of a finishing oil. After a shampoo and a conditioner, it’s essentially the third product you may consider incorporating – and it’s pretty easy to see why.

A good hair oil doesn’t just smooth frizz and add shine, but it can also help penetrate the hair and improve each strand’s condition over time. Such is the promise of the K18 Molecular Repair Hair Oil, the finishing oil offering from TikTok’s favorite damage-repairing hair brand. 

Read on for my full review.

What We Like

  • Actually sinks into hair, rather than sitting on top and coating it
  • Minimizes frizz and flyaways
  • Offers heat protection
  • Strengthens and hydrates hair

What We Don’t Like

  • May be too heavy for finer hair types
  • Higher price point

The Facts

  • K18 Molecular Repair Hair Oil
  • Best For: Dry or damaged hair
  • Can Be Used For: Straight, wavy, curly, and coily hair types
  • Cruelty Free? Yes
  • Key Ingredients: Avocado oil, sunflower oil, sh-Oligopeptide-78
  • Price: $65, though a trial size is available for $27
  • Size: 1 fluid ounce (or 0.3 fluid ounces for the mini)

About The Brand

K18 is a science-first hair brand, that uses technological advances to actually repair hair damage. The brand is named after its patented K18 peptide, which repairs damaged hair strands from the inside out. The K18 peptide fills in the gaps in the polypeptide chains which make up strands of hair, re-bonding the strand. It improves the condition of hair, not just the look of it.

The most famous and popular product from the K18 line is the Leave-In Molecular Repair Hair Mask, which is, as the name suggests, a leave-in mask that can be used in the place of a conditioner. The brand also offers shampoos and now, the K18 Molecular Repair Hair Oil.

About My Hair: Long, Damaged, and Sometimes Dry

K18 Oil Long
Annie Walton-Doyle / Timeless Hairstyles

My at-home bos dyeing habits have inflicted a certain low-level damage on my hair, exacerbated further by swimming in a chlorinated pool several times a week. My hair is naturally fairly soft and fine, but this harsh routine has left it in need of nourishment and moisture to help combat damage and frizz. 

I tend to wash with a cleansing yet hydrating shampoo, then either use a nourishing conditioner or a hair mask. Hair oils have been a mainstay in my repertoire for as long as I can remember, and if I don’t apply one before allowing my hair to air dry, the results are exceptionally frizzy and dry-looking.

I also credit hair oils with allowing my hair to stay long and (fairly) soft and shiny, in spite of the damage I inflict on it.

Upon reading the packaging of the K18 Molecular Repair Hair Oil, I was absolutely intrigued. The K-18 Leave-In Mask has been on my radar for years, and learning that the brand also offered a finishing oil with the same reparative science sounded highly appealing.

The instantaneous results combined with the way the K18 Molecular Repair Hair Oil is improving my hair’s condition over time is making this product a new hair oil favourite. 

The K18 Molecular Repair Hair Oil feel: Light As a Feather

The K18 Molecular Repair Hair Oil feels extremely lightweight when pumped out of the pipette bottle. This thinner texture had me feeling initially sceptical, as I just couldn’t see how something that felt almost watery could possibly add the gloss and moisture I needed. 

The K18 Molecular Repair Hair Oil also feels different from other hair oils in that it actually seems to sink into my hair, rather than sitting on top and providing a sort of glaze. Again, this left me concerned, as it almost seemed as though the product was disappearing after I applied it. However (spoiler alert) these fears were all unfounded…

How To Use The K18 Molecular Repair Hair Oil

K18 recommends using the K18 Molecular Repair Hair Oil in conjunction with their viral Leave-In Mask. After applying the mask and waiting for four minutes, you can apply your oil. It’s recommended that you then wait a further four minutes before applying heat or styling your hair as normal.

I have tried using the K18 Molecular Repair Hair Oil both alongside the mask, and as a part of my haircare routine more generally. I wash with shampoo, condition (or mask), and then apply about five drops through the mid-lengths and ends of damp hair.

I never heat style my hair, both because of laziness and because I don’t want to inflict any more unnecessary damage, so I then part my hair and allow it to dry naturally.

The Results: Nourishment and Shine

K18 Oil Long 2
Annie Walton-Doyle / Timeless Hairstyles

After allowing my hair to dry with the K18 Molecular Repair Hair Oil in it, my locks felt healthy and nourished and had a noticeable glossy sheen. It felt easy to brush and pleasingly soft to the touch.

After using the oil after washing several times, I’ve also noticed that consistent use seems to have a cumulative impact on my hair. The overall condition feels improved, and my hair feels stronger and overall happier!

The Scent: Gentle, but Pleasant

Aside from how my hair looked and felt after using the K18 Molecular Repair Hair Oil, the user experience is also pretty delightful. The product is scented, but only very lightly, and it’s a subtle, somehow expensive-feeling aroma.

The ingredients list does contain perfume, but I find the scent more a part of the application process than anything that lingers in the hair afterwards. You can apply your perfume without any fears that it’ll clash with your hair’s fragrance after it dries.

The Ingredients: Science Plus Nature

The K18 Molecular Repair Hair Oil is, as you’d expect from a K18 product, highly ingredients-focused. The range is built around its patented peptide, which offers some pretty impressive claims like 24 hours of frizz control and a 78% reduction in split ends.

This oil also harnesses the power of nature including avocado and sunflower oils to offer extra nourishment, shine, and moisture. Impressively for a frizz-control product, it’s silicone-free, making it suitable for fine and curly hair types, too.

The Value: You Get What You Pay For

Let’s face it: the K18 product range isn’t exactly bargainous. But if you’re on the lookout for something that can actually help to repair damaged strands over time, it’s certainly a range worth exploring.

I also think that the K18 Molecular Repair Hair Oil offers some of the best value within the range, as one bottle will take months (if not years) to get through. If you only use the recommended 3 drops every time you shower, a fluid ounce of this oil is a worthwhile investment on a cost-per-use basis. Plus, it does seem to offer more genuinely reparative properties than your average hair oil.

Similar Products: Reparative Hair Oils

The Olaplex No. 7 Bonding Oil is another great option for anyone wanting an oil that helps repair the hair’s individual strands over time. The Olaplex range is designed to treat weakened and brittle hair on a strand-by-strand level, repairing damage to boost strength. This oil does all that, while also offering a gloss and shine to locks after just one use. 

For anyone on a tighter budget, the L’Oreal Elvive Extraordinary Oil Deep Nourishing Treatment is a fantastic option. It doesn’t offer the bond-building qualities of the K18 Molecular Repair Hair Oil, but it does add some extra nourishment and helps reduce frizz for a soft and shiny mane.

The Final Verdict

For anyone looking for a hair oil that goes the extra mile, the K18 Molecular Repair Hair Oil is a wonderful choice.

From your first use, you’ll see a noticeable improvement in your hair’s quality – but what’s even better is the way this adds up over time. Anyone who bleaches, dyes, or excessively heat styles their hair could benefit from having this oil in their arsenal.

The Specifications

  • Brand: K18 Haircare
  • Product Name: K18 Molecular Repair Hair Oil 
  • Price: $27 – $65 each depending on which size you go for.
  • Size: 0.3 fluid ounces – 1 fluid ounce

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