I Tried Hailey Bieber's Favourite Hair Mask, and It Damn Well Works

When people start comparing a haircare product to Olaplex, I normally roll my eyes so hard. It’s an easy way to grab attention because Olaplex is the gold standard when it comes to hair repair and maintenance, especially for bleached or chemically treated hair. As someone who’s been balayage-ing my Afro hair for the past few years, I can honestly say it takes a lot for me to compare other products to parts of the Olaplex system because of how effective it is. Plus, much of the ingredient system is patented, so most things genuinely aren’t comparable. I first heard about K18 via U.S. beauty editors I follow who buzzed about its ability to transform bleached and damaged hair, but being the cynical Brit I am, I found it difficult to believe. Then, I tried the brand’s hair mask, and I was blown away.

Nothing about this mask makes sense to me, and I’m saying that in the kindest way. The size, the price, the application method… It’s all a bit of a head-scratcher, but once you try it, you are genuinely left with stunning results. It’s no wonder it’s one of Hailey Bieber’s go-to masks.

Before I get into it, let’s talk about what the mask is actually for. The full name is the K18 Leave-In Molecular Repair Hair Mask, and it claims to repair damage in just four minutes. Yes, four minutes. I have to say I’m not entirely sure how we’d measure this, as it is a leave-in treatment, so I couldn’t necessarily tell when it kicked in.

When referring to damage, we’re talking about chemical damage such as relaxers and perms, anything that's using harsh ingredients to reset the molecular bonds of the hair to change the shape; colour treatments, especially those that require you to pre-lighten your hair to remove pigment from strands; and then, of course, heat damage if you, like me, straighten or curl your hair more often than you ought to.

After using the K18 Biomimetic Hairscience Leave-In Molecular Repair Hair Mask.

K18 uses a patented peptide in its formula that can penetrate deep into the hair shaft and reconnect broken keratin bonds to make hair stronger and smoother. While a lot of masks and conditoners do help make your hair feel smooth, most will only work on the outer layers of the hair, and some even use ingredients to mimic smoothness without actually fixing the problem. Have you ever used a mask that feels great, but then you wash your hair, and it feels super tangly and dry? That’s because the conditioner you used sat on top of your hair but isn’t actually repairing from the inside, usually due to the silicone or silicone-like ingredients in the formula. This brings me to the first thing that’s a bit odd about this mask: You don’t condition before you apply it. You just shampoo, towel-dry and then apply.

When you’re used to shampoo and conditioner tag-teaming, this does feel a bit strange, but it makes sense, as you want to give the peptides the best chance at reaching your hair cuticle. Most people only need one pump of this to work—another thing that felt entirely wrong but worked for me.

I have mid-length, Afro-textured hair, and one pump was fine to apply from tips to roots and comb through. If you have longer hair, start with one and then do another if you feel like it’s not enough. The mask is small, and the price is high, but it’s very concentrated, so you really don’t need a lot to see a difference. I applied a heat protector straight after, as it doesn’t claim to be one, and then got to drying my hair.

I’m not one for theatrics (often), but I genuinely gasped when I felt how smooth my hair was and how little breakage I had after blow-drying and straightening. Plus, my hair looked shinier, and this was after just one use. K18 suggests using it for at least four washes to see the biggest difference, but if this is the impact after just one, I’m beyond excited to see how far this can take my hair.

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