Olaplex vs. K18: ‘I put the leading bond-builders to the test’
There’s a lot of buzz around bond-building treatments in the beauty world. They promise to repair damaged hair and boost resilience, for stronger, shinier locks.
And if you’ve heard of bond builders, you’ll probably have heard of Olaplex and its Nº.3 Hair Perfector, the original, patented leave-in mask. However, there’s a new pretender in town – K18’s Leave-in Molecular Repair Hair Mask. Some say it’s better and Rihanna’s already a fan.
As someone whose hair is particularly susceptible to damage (that will be all the heat styling and dye jobs), I was very keen to see if these viral treatments actually lived up to their claims. So, I decided to pit them against each other, trying each for two weeks (with a break in between) to see which strengthened and softened the best.
I also spoke to Anabel Kingsley consultant trichologist and brand president at Philip Kingsley about the benefits of bond-builders.
What are hair bonds?
Before delving into why you might need a bond builder, let’s get into what hair bonds actually are. “Our hair is made of protein fibres known as keratin,” says Kingsley. “Keratin is a powerful protein formed by the combination of eighteen different amino acids. Amino acids are an essential component of healthy hair as they combine to form proteins used by the body to build tissue cells.”
The chemical interactions between these proteins determine characteristics such as hair texture, colour, shine, and strength. It’s the hair bonds that act as a supporting wall between each protein chain to ensure these interactions can occur, so it’s essential to keep them strong and healthy. But, of course, many external factors can damage those bonds. Let’s break it down.
What breaks hair bonds?
Anything from heat styling to colouring and even brushing can cause bonds to break and hair to snap. “The main tell-tale signs of damage are dryness, brittleness, split-ends, breakage, frizz, dullness and tangles,” explains Kingsley.
I really started to see the impact of my broken bonds when I spotted long dark strands of hair collecting on my carpet, and I had to start vacuuming a lot more often, both of which were far from ideal. I tried installing a Hello Klean shower filter to protect against the dreaded hard water in London, but I felt like my hair needed to be built back up.
Luckily, there are products out there formulated specifically to help heal and mend our broken bonds (awww). Applying a heat protection spray when you’re using hair dryer or heat styler, along a hair oil to help rehydrate and reduce breakage, are advised. But the most effective way to treat damaged hair is by using a leave-in bond building mask.
So, what are bond builders?
“These are formulas that can repair broken bonds within the hair shaft,” says Kingsley. “When the hair’s outer layers are compromised (the lipid layer and cuticle), this can expose the hair’s cortex (where the bonds are found), causing them to become damaged, then weaken and break.”
Unlike hair masks, which only work to repair the hair cuticle externally, bond builders “help to repair bonds in the hair’s cortex, restoring its strength and resilience to damage and breakage.” Kingsley explains.
What’s the difference between Olaplex and K18?
Olaplex No. 3
Olaplex is probably the first brand you think of when it comes to bond-building products. Its patented technology was groundbreaking when it first launched back in 2014, promising to soften and strengthen strands, and it still lines the shelves in prestige salons and beauty insiders' bathrooms 10 years later.
Like all Olaplex products, the No.3 Hair Perfector contains a molecule called bis-aminopopyl diglycol dimaleate – it sounds complicated, but its job is simple; it works to repair broken hair bonds, with the help of strengthening amino acids, hydrating squalene and nourishing ximenia oil.
“Together, these ingredients restore moisture-imparting lipids naturally found in hair, offering weightless conditioning, detangling and shine, without leaving behind unwanted residue or build-up,” Mark Coates, director of education at Olaplex, tells us. “This is the only product [on the market] offering instant and continuous multi-level repair, ensuring optimal hair health from the cortex to the cuticle,” he adds.
K18 Molecular Repair
K18 first landed on the haircare scene back in 2020, and it’s certainly given Olaplex a run for its money.
The molecular repair mask is formulated with the brand’s patented biotech-developed peptide, which repairs damaged hair bonds by reconnecting broken polypeptide chains at a molecular level. This means it works on all hair types, as at this level, all hair is the same.
Jordan Alexander, the director of education at K18, claims there aren’t any other products that repair hair to quite the same standard. “We spent ten years mapping amino acid sequences across the entire keratin genome that makes up human hair, until we discovered one unique sequence (a bioactive peptide) that brings damaged hair back to its original, youthful state,” he explains.
“K18 is often compared to other bond builders, but really our products do much more than simply repairing bonds and, as you don’t need to wash it off, damage is being repaired for longer, so the results have more longevity too.”
How I tested
I started with the Olaplex No.3, using it a couple of times a week on pre-shampooed, damp hair, for two weeks. I assessed how quickly I noticed the promised softening effects, as well as the packaging design, ease of use and any differences noticed after the two-week trial period.
After a two-week bond building hiatus, I then applied the K18 four times consecutively across another two-week period, to give my hair that first initial hit of reparative ingredients, according to the brand’s advice. “When you first start using the K18 treatment you want to use it consecutively for 4-6 washes, depending on your hair damage,” advises Alexander. “Then you can drop back to as needed, once a week or once a fortnight, or whatever feels right for your hair.”
Again, I considered the product's claims – such as reversing the dry, brittle and knotting effects that come with hair damage, and leaving hair soft, shiny and more elastic – and whether it delivered on them.
Olaplex vs K18: My honest review
Ease of use
Following the instructions, I applied the Olaplex No. 3 mask to pre-shampooed damp hair, and let it sit for ten minutes. I’d be lying if I said this wasn’t a slight inconvenience, especially on a post-work, hair wash day where I want to get the job done as quickly as possible to avoid eating into my valued (and short-lived) rest time. On a few occasions, I ended up using a spray bottle to dampen my hair to avoid getting in and out of the shower first.
K18 has a different application process as it’s used post-shampooing, in place of a conditioner. This made it an easier, more seamless step in my hair wash routine, which I appreciated. As someone with long, curly, tangle-prone hair, I was sceptical about skipping out on the added dose of hydration from my beloved conditioner. But, somewhat surprisingly, I was able to brush through my hair easily, without any break-inducing tangles.
K18 wins this round!
First impressions
Obviously, you should never judge a book by its cover, or in this instance, a bond builder by its packaging. But both are good-looking products, with clean, simple packaging. I liked their fuss-free, clinical look, which I hoped also reflected the formulations inside.
I've used Olaplex before and didn't think I'd be swayed by a new pretender, to be honest. With a thick texture, it feels indulgent and has seen me through two rounds of going blonde, always leaving my hair looking, feeling and smelling good.
The K18 is slightly runnier and thinner in consistency, which made me second guess its ultra-nourishing benefits for a minute. The impact wasn’t as instantaneous, either. Clearly, more patience and consistency are key for unlocking the longer-term results with this product.
The results
Speaking of which...
I rinsed and repeated (quite literally) with the Olaplex No.3 twice a week for a fortnight, and by the end of the trial period, my hair felt softer and more elastic, which meant less breakage – much to my absolute delight, not to mention my carpet and poor, hardworking hoover.
It promises instant results and it genuinely delivers. Though there was a slightly inconvenient ten-minute wait after applying, it gave me softer, shinier hair after the first use. My once dry and frizzy strands looked and felt smoother for longer when I blow dried my hair, too. It wasn’t just me who noticed the transformation either, as my housemate also complimented my glossy locks not long after I started using it. And lo and behold, the bottle seemed to empty at a faster rate after they discovered my smooth hair secret...
It did a great job of adding shine and eliminating dryness. I also noticed that my hair wasn’t as tangled, which meant far less breakage while brushing, and less clawing out clogged fur balls from my hairbrush. An indisputable win.
When it came to using the K18, I wasn’t expecting to see and feel the results as quickly as the No.3. But after a couple of washes, I could tell that the peptide-packed formula was already getting to work. I found that my hair was easier to brush (wet or dry) and, in turn, less susceptible to breakage – it had clearly increased my hair’s elasticity and helped to repair my once dry and brittle ends.
To reap the full benefits, I’ll need to reapply every 4-6 washes. But with the boost in hair health (and compliments in the office), I’m fully invested.
My final verdict: Olaplex vs. K18
It’s clear how and why both products have earned themselves a seat at the hair-softening table.
For me, the K18 swayed me slightly more as it worked more seamlessly into my shower routine. Unlike the No.3, it didn’t need damp hair for application and there was less waiting around and rinsing. Instead, it simply replaced my conditioner a couple of times a week. But if I was a more patient person (one day!), Olaplex was definitely worth the extra effort on hair wash day – I was truly impressed with its softening effects, and the fact that other people began to notice should be good enough reason to put the time in.
As they’re both great products that show clear results, price point has to be a consideration. A 50ml bottle of K18 retails at £70 but the slightly higher price tag really does reflect the high-quality product and fantastic results.
For half the price and double the product (£28 for 100ml) the No.3 is a bit of a steal. It's ideal for maintaining healthy hair or strands that aren’t as severely damaged. The quick results are great for times when you feel like your lengths could do with a bit extra TLC, such as after colouring or in between haircuts.
As someone with hair particularly susceptible to breakage (thanks to the ‘ol colouring and heating styling) I’ll be continuing my K18 journey but keeping my Olaplex proudly in the bathroom for in-between times. If someone in my house doesn’t get to it first, that is...
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