K18 vs Olaplex: which hair treatment is better?

Two treatments are battling for the hair repair spotlight: K18 vs. Olaplex. Both work in a different way than most hair care products (more on that later) and both have caused a stir. But who reigns supreme? We’ve put the hair heroes head-to-head to find out.

Ten years ago, every one of the best hair masks and scalp treatments focused only on treating the outer layers of the hair cuticle. Then, in 2014, came Olaplex, a revolutionary bond-building treatment that works from the inside out to repair damage and strengthen strands. It quickly became a staple at every major salon with stylists, beauty editors and celebrities alike speaking lyrically about its mane-changing results.

Since then, several beauty brands have attempted to replicate Olaplex’s patented technology, but none could match the cult brand’s restorative powers – until now. Launched in 2020, K18 offered an alternative at-home hair mask, which also works on a molecular level, to restore and repair dull locks while salons are closed. It was quick to impress and many are now wondering which treatment to beat between K18 vs Olaplex? We have answers.

K18 vs Olaplex: which treatment is better?

What are K18 and Olaplex?

Between 2014 and 2018, the Olaplex line consisted of three products: No. 1 (an additive used during salon color application to reduce damage), No. 2 (an active cream treatment applied to the hair after coloring, in salon), and No.3 (a diluted version of No.2 that clients can take home). It’s the latter, the #3 at-home treatment, that remains a best-selling cult classic despite the brand launching one of the best shampoos and conditioners, a hair mask, and several other at-home strengthening treatments.

More recently arrived on the hair scene, K18 was born in the United States. Currently a one-product wonder, the K18 Leave-In Molecular Repair Hair Mask promises to repair damage caused by bleach, color, chemical services and heat – restoring strength, softness and bounce to hair. As with Olaplex No.3, K18 is an at-home treatment – but is also used in several salons around the world.

How does science work for everyone?

Developed by California scientists, Olaplex’s famous formula is powered by a single active ingredient: bis-aminopropyl diglycol dimaleate. This ingredient, which is patented and exclusive to Olaplex, permanently rebuilds broken disulfide bonds in the hair, reducing damage from chemical services as well as damage from heat styling, even the best straighteners and the best curling irons as well as environmental aggressors.

Also backed by scientists, K18 features a single key ingredient: the brand’s patented K18 peptide. This peptide has a unique sequence of amino acids that deeply penetrate hair to reconnect broken keratin chains for smoother, stronger locks – like an at-home puffy keratin treatment that also repairs. Although hero ingredients differ, K18 and Olaplex work from within to repair damage caused by bleach, color, chemical services and heat. Want to go even more in-depth on the science bit? Our beauty editor’s K18 review has a deep dive on ingredients.

Main differences between K18 and Olaplex

A woman's hand rubbing a hair treatment into her wet hair

(Image credit: Getty images)

  • Application: K18 is a leave-in formula – best applied to freshly washed, towel-dried hair. Olaplex No.3 is a pre-shampoo treatment that is designed to be left on for ten minutes before washing out.
  • Ingredients: Olaplex Bis-Aminopropyl Diglycol Dimaleate rebuilds broken disulfide bonds, while K18 Peptide repairs broken keratin chains.
  • Time: While Olaplex No. 3 should be left in place for ten minutes or more, K18 should be left in place for four minutes before styling as usual.
  • Price: Olaplex No. 3 retails for $28/£26 for 100ml and K18 is $75/£55 for 50ml.
  • Hair type: Both treatments are suitable for all hair types.
  • Results: Both hair treatments have the power to transform hair, delivering soft, silky locks that look healthier with every wash.

K18 vs. Olaplex: W&H Verdict

Olaplex No.3 is the original bond-building treatment with impressive, patented hair technology and results that speak for themselves. Many of the top hair products have tried to replicate this technology, but have failed. Except, of course, for K18. Although the ingredients differ, the patented K18 peptide is equally impressive – rebuilding and repairing the damaged keratin chains that form the main component of our hair.

The main differences between the two treatments are price and application. Costing $28/£26 for 100ml, Olaplex is by far the cheaper option of the two. However, with the K18 mask, you’ll find that a little really goes a long way – with two pumps proving to be more than enough to cover an entire head, provided you have a medium or shorter hairstyle.

The K18 has advantages for ease of use. The mask is designed to be applied after shampooing and left for four minutes before styling as usual, without rinsing. Olaplex No.3 is a pre-shampoo treatment that can be applied directly to towel-dried hair for 10 minutes, then rinsed out with shampoo and conditioner before styling.

All in all, you can’t go wrong with either of these mane changing treatments that are a brilliant addition to any hair care regimen. If your hair is color-treated, dry, or damaged – give these treatments a spin, pronto – you’ll be blown away by the results. As for which one is better – we’ll cheat and call it a draw.

K18 vs Olaplex: Shop Hair Care Heroes

David R. Brewer