Olaplex vs K18 (The Definitive Guide)

Olaplex is a brand loved and used by hair stylists up and down the country, and you’ll often be offered it as a way to strengthen and protect your hair.

But how does the Olaplex No.3 hold up against the hugely popular K18 leave-in molecular repair hair mask? Let’s find out in today's comparison: Olaplex vs K18!

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Olaplex No. 3 vs K18 Molecular Repair

For anyone with even remotely damaged locks (that’s most of us), it’s a good idea to address the damage every once in a while with a hair treatment. Even better, though, would be to stay on top of it by treating your hair regularly.

For a simple at-home treatment, you have loads of options. Some products you put in your hair multiple times a week, and some products you only use once a month, sometimes less. Two great treatments to address damage are the Olaplex No. 3 and the K18 Leave-in Molecular Repair Hair Mask.

Both products are suitable for all types of damaged hair, but those with treated or colored hair will see the most benefit. Hair coloring services are steadily becoming more and more gentle, but it's impossible to get away from the fact that dyes and bleach are inherently damaging.

Olaplex No.3 is recommended for use alongside their No.0 treatment, and when used as the intended two-step process, you can expect your hair to be up to *three times stronger* than before. When used on its own, No.3 can still reduce breakage and helps to visibly strengthen hair. Olaplex No.3 is part of the complete Olaplex system, and the products are recommended to be used together rather than as standalones—something to consider before buying.

The K18 leave-in molecular repair hair mask uses a patented bioactive peptide hair treatment which supports and strengthens hair elasticity, as well as repairing damage from heat styling, chemical and coloring services. Unlike Olaplex, it can be used as a standalone treatment, and it can be used with the shampoo you have at home.

We all know that we want our hair routine to be as quick and easy as possible. The K18 is a leave-in mask. Once you have shampooed, you simply towel dry your hair, apply the hair mask, and leave for four minutes to activate the repair technology (before styling as normal). It is an easy product to build into your hair care routine, and only needs to be used on a weekly basis.

Olaplex No.3 is also used once a week, and is applied to damp hair before rinsing out and shampooing and conditioning as normal. It’s an easy enough routine, and users typically see results quickly. We love that there are *tonnes* of before-and-after examples to showcase exactly what you can expect.

Olaplex are also big on helping the planet and offer useful info on how much water they use to create their products, and how by not using secondary packaging—such as a box—they are saving 44,000 trees a year from being cut down. Nice little facts which help you feel a little better about what you are buying.

K18 also has a strong sustainability promise entailing a radical reduction in waste and plastic, although you have to do a little digging to find it.

Finally: pricing. The K18 hair mask will set you back $75 for a 50ml bottle, whilst you will only need to spend $30 for a 100ml bottle of Olaplex No3. K18 also comes in a 5ml trial size, and 15ml bottle too, which is handy if you haven’t used it before and just want to sample it.

Final Verdict

Overall, we love both of these products. Their patented technology allows you to strengthen and protect your hair from heat and color damage, as well as the stresses of daily life. Both are easy to incorporate into your weekly hair routine and have an easy guide on how to use on the website.

Other than the obvious disparity in price point (with the K18 leave-in molecular hair mask being a fair bit more expensive per fluid ounce), both hair masks are a solid option when wanting to repair damaged hair.

Ultimately, if you're looking for a standalone treatment, K18 is for you. If you're looking for a full haircare routine, though, then Olaplex has your name on it.

To round off our review, here are our recommendations for the other best-selling ranges and products that Olaplex and K18 offer.

Olaplex Best-Sellers

Step 1:
Try the No.3 Treatment

Step 2:
Try the No.4 Shampoo

Step 3:
Try the No.5 Conditioner

K18 Best-Sellers

For hair repair:
Try Molecular Repair

For clarifying:
Try Detox Shampoo

For frequent washing:
Try pH Maintenance

This article was originally published on December 7th 2022, but it has been reviewed and updated with the latest available information on February 26th 2024 by Sara Mckay, MA.