I Tried K18, the Better-Than-Olaplex Mask, and It Saved My Damaged Hair

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We tested the salon-loved K18 hair mask to see if it really holds up to heat- and color-damaged hair. Spoiler alert: It exceeded our expectations.

Rd Editor Tested K18 Madi Koetting/rd.com

I’m a curly-haired girly, and my strands have undergone several phases through the years. First, there was the straight-hair-obsessed phase of my younger years, when the only power tools in my beauty arsenal were my flat iron and blow-dryer (the heat damage was REAL). Then after finally accepting that curly hair is a gift—not a curse—I leaned into all the masks, serums, shampoos for my hair type, and best frizzy hair products to feed my curls with the hydration it lacked. At this point, I’d mastered the curly-girl technique, but I wanted a break from my brunette roots.

Two summers ago, still obsessed with mainstream hair trends, I wanted nothing more than to achieve the sun-kissed, blonde balayage look. I wholeheartedly leaned into the balayage process, returning to the salon every three months to get my blonde strands beautified and lightened. I rocked the blonde look for a year and a half before realizing that my curls weren’t quite as full, bouncy, or hydrated due to all the color damage they’d undergone. So when my hair colorist told me about K18, a leave-in hair mask with a one-of-a-kind peptide technology that revives hair damaged by heat and color, I knew it was time to return to my brunette roots and give K18 a whirl. After all, hair that is happy and healthy is the most beautiful.

What is K18?

K18 is a leave-in molecular repair mask (emphasis on leave-in) that strengthens, soothes, and hydrates heat- and color-damaged hair. And it only takes four minutes after combing it through clean, wet hair to work its magic. The catch, however, is that K18 only works when hair isn’t conditioned. Meaning, you’re supposed to skip the conditioner after shampooing your scalp to reap the benefits.

Unlike other hair masks, K18 is formulated with a patented peptide technology. Meaning, it’s a highly concentrated formula that targets hair molecules to give you the healthiest, bounciest strands of your life. And yes, it’s 100 percent safe to use at home. Amazon and Sephora reviewers are raving about its speedy technology that instantly transforms strands from stringy to strong and bouncy—regardless of hair type.

The treatment is often compared to the cult-favorite product Olaplex Hair Perfector No. 3, which I used for a year prior to testing K18. When my colorist told me K18 was like Olaplex but with more advanced technology, I knew it was time to put it to the test.

How we tested it

before and after side by side comparison using k18Madi Koetting/rd.com

Because I only wash my hair once or twice per week (once is ideal, but sometimes my strands need some TLC before then), I planned a hair-wash day at the beginning of the week and got to work on my K18 test. I brushed out my hair, which had undergone some heat damage from straightening it the week prior, and hopped in the shower for a full rinse and shampoo.

While it’s recommended to use a clarifying shampoo before using K18 to remove buildup, I didn’t have one handy. Instead, I lathered my scalp with the Aveda Color Conserve Shampoo, which I use once per week to protect my fresh brunette color from a recent dye job. Now, I won’t lie. I seriously debated using conditioner after I rinsed my scalp from the shampoo. The reason being, I hate the texture of my hair when it’s not properly moisturized or conditioned (who doesn’t?). I gave my conditioner a long stare, thought about the consequences, and put all my strength into my K18 hair mask to save my brittle strands.

After giving my head a thorough rinse, I squeezed out the water and dried my hair with a clean T-shirt (I prefer using a clean, XL T-shirt over a towel to protect my curls from frizz, which is often caused by the friction of drying with normal bath towels). Because my hair didn’t have conditioner, I carefully brushed through it, roots to ends, until it wasn’t a tangled mess. I squeezed out the excess water in my hair once more, and then it was time to apply the K18 hair mask.

I started with one full pump of K18, combing and scrunching it through one half of my hair from middle to ends. I applied another full pump of K18 to the other half of my hair. To top it off, I applied a third and final pump, paying extra attention to my roots and ends.

After letting it sit for four minutes, I saw my curls start coming back to life, although they were still damp, so it was hard to glean any visible results. While there’s no recommended way to dry your hair with K18, I’m a firm believer that the drying technique you use has a significant impact on your end result—regardless of the products you use. I prefer the plopping method, so I threw my hair up in a T-shirt for 20 minutes before letting it air-dry.

One hour later, my hair was done air-drying, and I could already tell how much fuller and stronger it felt before taking a look in the mirror. Much to my delight, my hair looked—and felt—stronger, happier, and healthier than ever.

K18 product features

Pros

What I like about K18:

  • Holds hair like a gel, and moisturizes like a cream
  • Takes just two to three pumps to soak in, making the bottle last for months
  • Takes just four minutes to activate (no rinse needed)
  • No conditioner is needed in the wash cycle—K18 is that strong!
  • Formulated for all hair types, working particularly well on medium and thick hair
  • Patented peptide technology sets it apart from standard hair masks
  • Silicone-free
  • Clean and cruelty-free

Cons

Consider these factors before you buy:

  • At $75 for a full bottle, this hair mask is on the pricey side
  • Because K18 is applied to unconditioned wet hair, extra care and attention is needed when brushing your hair

FAQs

Is K18 organic?

No, K18 isn’t organic, as it uses natural and synthetic ingredients for the peptide to soak into hair. K18 uses a blend of fewer than 15 ingredients. While it’s not quite organic, the brand notes it’s clean, cruelty-free, and formulated without silicones.

Why can’t I condition my hair before using K18?

I know, I know. It’s really difficult to withhold the urge to condition hair before using K18—especially if you have dry and damaged hair. The reason conditioner is a big no-no with this product is that K18 can’t penetrate the hair cuticle to fix the keratin bonds if conditioner is applied first.

How often should this product be used?

It’s recommended to use K18 for six consecutive washes when starting out. From there, it can be used every two to four washes, depending on how often you wash your hair. If you wash your hair once per week (like curly-haired me), I recommend using it every wash.

What shampoo do you use with K18?

Any shampoo is safe to use with K18. Reviewers have found that they’ve experienced the best results after using a clarifying shampoo. I recommend using a silicone-free clarifying shampoo at least once per week to remove oil and buildup before using K18.

Can you use on colored hair?

Reviewers with colored hair have found that K18 is safe to use on colored and highlighted hair. (I’ve used it on my dark brunette-dyed hair, and it hasn’t dulled the appearance of my color or lightened it.)

What other reviewers have to say

K18 has more than 2,000 Amazon ratings and a 4.2-star rating. Here’s what other reviewers have to say about it:

Verified Amazon purchaser Christia writes, “Just finished bleaching my hair and used K18, and goodbye Olaplex! Olaplex never really worked for me anyway, and K18 does! Hair is beyond soft, and I’ve got zero breakage, and I’ve bleached my hair for over two decades.”

“I was slightly skeptical about using such a small amount of product following a wash with a detox (clarifying shampoo),” shares Linda. “My hair is normally a rat’s nest without conditioner. I applied the product, ends to roots, thoroughly working it into the strands, and waited the full four minutes. My hair was so much healthier. The difference with one treatment convinced me to purchase a full size.”

One Sephora reviewer attests to its powerful technology: “My colorist recommended this to me in the salon before Sephora even carried it. She said it was invented by the same people who made Olaplex, and that this was another level above Olaplex, so I decided to try it. I’ll never go back! My hair was super bleach fried, heat damaged, dry dry dry. I have really thick and long hair and use just three pumps. My hair comes out so soft and bouncy.”

Final verdict

I’m still on my curly-girl journey to revive my hair from all the heat and color damage it’s undergone in recent months. And I’m thrilled to have K18 in my beauty arsenal to help revive my curls. The peptide technology of K18 is unlike any other hair product I’ve used, making the investment in this mask absolutely worth it. Plus, it’s strong enough to double as a leave-in conditioner, hair gel, and cream all in one—no need to layer on extra products. Whether you have straight, curly, wavy hair—or a mix of the three—K18 is for every hair type that’s experienced more heat and color damage than they care to admit.

Where to buy

Rd Ecomm K18 Via Amazonvia merchant

If you’re ready for the best hair of your life, the K18 molecular leave-in hair mask is available on Amazon and Sephora for $75.

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Madi Koetting
As Associate Shopping Editor, Madi is an expert at helping Reader's Digest readers find everyday household products to level up their life. She covers everything from Instagram-famous products to the internet’s best deals and discounts. When she’s not deep in a story, you can find her honing her at-home mixology skills and scouring TikTok for the next trendy product.