K18 vs Olaplex Review: Which bond builder is better?
K18 and Olaplex are powerful hair bond builders widely touted as the most effective on the market. Both promise to repair damaged hair, but they work with different active and in very different ways. So which one is better value?
I’ve put both to the test, you can read the Olaplex review here and the K18 review here, but this is more of a side-by-side analysis so you can work out which one might be better for you.
What do bond builders actually do?
Olaplex No. 3 Hair Perfector is part of the larger Olaplex hair treatment range and works to temporarily repair disulphide bonds in the hair. These are the bonds that break when you bleach, dye, or heat-style your hair to death. Olaplex’s ingredient, Bis-Aminopropyl Diglycol Dimaleate, works on a molecular level to restore strength and structure.
K18 Leave-In Molecular Repair Hair Mask claims to go deeper than surface-level fixes. It uses a bioactive peptide, the K18Peptide, designed to reconnect broken keratin chains—essentially repairing hair from the inside out. It's marketed as a lasting, progressive treatment that apparently reverses damage in just four minutes.
Does K18 fix split ends?
The only thing that repairs split ends is scissors. Repairing a split end is a bit like tearing a blade of grass through the middle and trying to put it back together. It won’t work. However, you can nourish your hair properly to prevent split ends. This is where bond builders come in.
K18 helps strengthen and smooth hair, which can reduce the appearance of split ends—but it won’t glue them back together. For true split-end removal, a trim is still your best bet. That said, K18 can help prevent future splitting by making the hair stronger and less prone to breakage.
Does Olaplex fix split ends?
Similar story. Olaplex No. 3 Hair Perfector doesn’t fix split ends, but it helps improve the overall integrity of the hair. The bond-building action may reduce how often split ends occur, especially with regular use.
Does K18 help hair grow?
K18 doesn’t stimulate hair growth directly. What it does do is strengthen hair so it breaks less, meaning you keep more of the length you already have. If your ends tend to snap off, K18 might help you hold on to inches longer.
Does Olaplex help hair grow?
Same deal. Olaplex hair treatment isn’t a growth serum, but it can support length retention by reducing damage and breakage. Healthier hair equals less trimming and more visible growth over time.
Is K18 a protein treatment?
Not in the traditional sense. While K18 works similarly to protein treatments by reinforcing the hair structure, it doesn’t contain actual protein. Instead, it uses a patented peptide to mimic and repair keratin chains from within. It’s designed to avoid the stiffness that can come from traditional protein overload.
Is Olaplex a protein treatment?
Nope. Olaplex 3 Hair Perfector is not a protein treatment either. It works on broken disulphide bonds—different from keratin or protein bonds—so you can use it even if your hair is sensitive to protein-heavy formulas.
How to use K18 and Olaplex
Olaplex No. 3 Hair Perfector: Apply to damp, towel-dried hair before shampooing and conditioning. Leave it on for 10 minutes or longer, rinse, then follow with your regular wash routine. It’s CG-friendly and safe for all hair types.
K18: Shampoo, do not condition, towel-dry until damp, then apply 1–3 pumps of the mask from roots to ends. Wait four minutes, then style as usual. Do not not rinse. In all honesty, this was problematic for me.
Which one lasts longer?
Olaplex isn’t permanent, but the effects stick around longer than one wash. With consistent use, it builds on itself and really helps improve the health of your hair over time.
K18 markets itself as a long-term fix that fixes your hair from the inside out, particularly with regular use.
Price breakdown
Olaplex No. 3 (100ml): Around $30–$40.
K18 Leave-In Mask (50ml): Roughly $75, with a 5ml trial size around $16.
When I tested them both out, I needed to use more Olaplex to properly detangle my hair and get a brush through it, but not a huge amount. With the comparatively lower cost, that’s justified.
You’re not supposed to use a huge amount of K18, but I found it incredibly difficult to use on hair that was not conditioned. To try and get a brush through it, I needed to use more product. For the price, I didn’t think the amount I had to use was justified.
K18 v Olaplex: A Comparison
| Feature | Olaplex No. 3 | K18 Leave-In Mask |
|---|---|---|
| Best for | Bleached, dyed, heat-damaged hair | Bleached, chemically treated, or heat damaged hair |
| Application | Rinse-out treatment | Leave-in treatment |
| Slippage | High slip, detangles easily | No slippage |
| Key Ingredient | Bis-Aminopropyl Diglycol Dimaleate | K18Peptide (bioactive peptide) |
| How long does it take to work? | 3-10 minutes, rinse out | 4 minutes, leave in |
| Where is it made? | USA | USA |
| Split ends? | Helps prevent, doesn't fix | Helps prevent, doesn't fix |
| Hair growth? | Helps retain length | Helps retain length |
| Protein treatment? | No | Not technically, but similar effect |
| Price | $30–$40 | $75-$120 |
| Bottle Size | 100ml | 50ml-100ml |
My experience
Olaplex No. 3: This one made my hair feel smoother, shinier, and way easier to detangle after the first try. It didn’t magically heal my hair overnight, but after a few weeks of using it every other wash, I noticed less breakage and frizz. My hair held moisture longer and didn’t feel like straw by day four. There was also significantly less hair in the brush.
K18: This did not start off well. The first time I tried it, I followed the instructions exactly—no conditioner, damp hair, four-minute wait. My curls were flat, dry, and felt like hay. Detangling was awful. Three days later, I had to wash again because my hair was so matted.
I gave it another go a few months later—this time after conditioner, applied to soaking wet hair. And honestly, that worked better. My hair felt good that day. But the more I used K18, the more I noticed my hair getting dry and brittle again. You can read more about that in my K18 review.
Verdict
If I had to pick between K18 and Olaplex, Olaplex easily wins. It’s more affordable, the bottle is larger, it detangles your hair, and works with your regular hair care routine. It actually made my hair feel healthier. K18 might work wonders for some, especially those with extreme chemical damage, but for me it wasn’t worth the hassle or the price.
But everyone’s hair is different. Some people swear by K18. If you’re curious, I’d say start with the sample size.
