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White K18 Leave-In Molecular Repair Hair Mask bottle, 50 ml, with a black cap

The real product. The opinion is still ours.

HairproductK18

Four Minutes and You Do Not Rinse

K18 Leave-In Molecular Repair Hair Mask, the 50 ml (1.7 fl oz) bottle: a peptide treatment that stays in, for hair that has met bleach, color, or a flat iron with ambition.

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Added October 3, 2026 · 0 looks · 0 clicks

Why we love it

Most hair masks want a shower, a timer, and a rinse you will forget. K18 wants four minutes and then you style it. Shampoo, skip the conditioner, towel-dry, pump, wait. The mask stays. That is the whole plot, and the plot is the reason people keep the little white bottle.

We love the 50 ml one because it is the full-size bottle, not the sample that runs out during the apology. K18’s peptide is the brand’s whole argument: damage from bleach, color, chemical services, and heat, addressed in the time it takes to find a shirt. One to three pumps, ends toward the roots, four minutes, do not rinse. When we looked, Amazon had it at $75, in stock, ships from Amazon, sold by K18 Hair.

It will not replace a haircut. It will make the hair you already have stop negotiating with the weather. Olaplex can keep the bond-building shower. This one stays in.

The longer story

This is the K18 Leave-In Molecular Repair Hair Mask in the 50 ml (1.7 fl oz) bottle, model K18-31005. The brand’s notes: a leave-in treatment with the patented K18PEPTIDE, meant to repair damage from bleach, color, chemical services, and heat. Directions on the brand page: shampoo, do not condition, towel-dry thoroughly, apply 1 to 3 pumps from the ends toward the roots, wait 4 minutes, do not rinse, then comb and style. Use it for several washes after a salon service, then as needed. It is a mask, not a conditioner you rinse, and not a styling cream you pile on for volume.

Good for

  • Hair that has been bleached, colored, or ironed into a mood
  • A repair step that fits between the shower and the door
  • Anyone whose mask currently lives in the shower and never gets rinsed on time

Skip it if

  • You wanted the 15 ml mini, a trio, or a rinse-out conditioner. This page is the single 50 ml leave-in
  • Your hair is happy and you wanted a scent. This is a treatment, and it is not trying to be a perfume
  • You will condition first. The brand says skip the conditioner so the peptide can do the job

When we looked, it was $75, in stock, ships from Amazon, sold by K18 Hair. The price moves. The deal link is the Amazon page (/dp/B0961ZS96M) with our Amazon Associates tag threepaths-20. Confirm the size says 1.7 fl oz or 50 ml, one bottle, before you check out.

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