This at-home hair mask has been dubbed a better version of Olaplex—here's my honest thoughts (2025)

Let me introduce myself. My name is Grace, I'm a beauty writer, and I have been bleaching my hair for years. As a naturally dark brunette, I have been getting blonde highlights for as long as I can remember to help brighten up my lengths.

However, recently I have started to notice the damaging effects of said bleach. I'm talking breakage, brittleness and more. So, in a bid to bring my hair back to life, I decided to try out one of the best hair masks.

I had used Olaplex and various other brands for a long time, but I was ready to switch things up and try something new. Enter stage right, the K18 Leave-in Molecular Repair Hair Mask. Dubbed a better version of Olaplex, and used by the likes of Hailey Bieber and Rihanna, this mask has got somewhat of a celebrity status in the beauty world.

I have to admit, when it first landed on my desk, I was pretty sceptical. Unlike other hair masks, this is a leave-in formula that you don't rinse out. The idea of leaving a bond-repairing treatment in my hair had me feeling uneasy. Would it make my hair greasy? Would it weigh it down? And, most importantly, would it leave it more brittle from overload? There was only one way to find out.

My review of the K18 Leave-in Molecular Repair Hair Mask

K18 vs. Olaplex

First things first, what is the difference between K18 and Olaplex? When it comes to K18, the hair treatment itself is infused with the brand's unique patented K18Peptide, which works on a molecular level to repair damage. According to the brand's website, the peptide "mimics hair's structure to reverse damage by reconnecting polypeptide chains and disulfide bonds broken during bleaching, color, and chemical services."

By reconnecting these polypeptide chains, the mask strengthens along the length and width of the hair, offering a full 360 approach.

In comparison, Olaplex uses patented Olaplex Bond Building Technology™ , that rebuilds broken disulfide bonds to restore strength. The brand's popular weekly pre-shampoo treatment repairs and prevents damage, whereas the K18 mask works to restore your hair to its previous state.

Although the technology is seriously impressive, it's worth considering the difference in size and price. The K18 hair treatment is definitely more of an investment. Look at it this way, you can get 100ml of the Olaplex No.3 Hair Perfector for £22.40 (yep, it's currently on sale), whereas the K18 mask will set you back £53 for 50ml. If you're after a more affordable alternative, shop the Olaplex mask below. That being said, I definitely use less of the K18 mask on my hair, so I do get more for my money.

My verdict

The K18 hair treatment is meant to work from the very first use, so it was time for me to give it a go. After using a detox shampoo to remove any product buildup throughout the week, I followed the instructions on the back of the bottle and skipped my usual conditioner in favour of the mask. The bottle says to towel dry your hair after showering, then apply the mask and wait for four minutes before styling.

The texture was similar to the Olaplex No.3 Hair Perfector, and I liked the fact that the bottle had a pump, making it a lot easier to get the product out. I have very thick, naturally curly hair, so I applied a good 3-4 pumps to the ends.

It's worth noting that the brand recommends working it into the hair from the ends to the roots, however I did actually avoid the roots at first as I was worried about them looking (and feeling) greasy.

After waiting for four minutes, I blow dried and straightened my hair, and wow. My hair had truly never felt so soft or looked so sleek. Sure, I'd used other products in the past that had helped the condition of my locks, but this was on a whole other level. My hair looked good, it felt good and most importantly for me, it was way more manageable. I've now been using it for the past month, and the results just keep getting better. I've also noticed a shine to my hair that I haven't seen since getting it bleached, so this product will definitely be a staple in my routine for years to come.

It goes without saying that I'm obsessed - and keen to try more out from the brand. We've rounded up our top K18 products so be sure to check out our editor-approved buying guide, or simply shop our top picks for yourself below:

Shop the best K18 products