K18 vs Sebastian NO.BREAKER: How They Differ and Which Suits Your Hair

Updated November 2026. UKIYO prices are our live online prices; other brands' prices are NZ RRPs we checked in November 2026.

K18 is the one clients bring up after Olaplex. In NZ "k18 hair mask" gets searched more than almost any other repair product. We don't stock it. We sell Sebastian NO.BREAKER and Penetraitt, so this is written by people who sell the other option. We've stuck to what each brand says its product does.

How K18 works

K18's best-known product is the Leave-In Molecular Repair Hair Mask. K18 says its patented K18Peptide repairs damage from bleach, colour, chemical services and heat. The method is specific, and it matters: shampoo, skip conditioner, towel-dry well, apply a small amount, wait four minutes, then style without rinsing. K18 suggests using it for the first four to six washes after a chemical service, then every three to four washes. It comes in 5ml, 15ml and 50ml, and the 50ml is $149 RRP at the NZ stockists we checked.

What K18 does well is low effort. One step, every few washes, from a small bottle.

How NO.BREAKER works

NO.BREAKER spreads the work across the wash. Sebastian's claim is up to 20x stronger hair against breakage when the range is used together. There's the Pre-Shampoo Crème ($36.92), the Bonding Shampoo ($50.12), the weekly Melting Mask ($51.88), and two leave-ins: the Leave-In Cream ($63.32), which Sebastian says protects to 230°C, and the lighter Treatment Spray ($63.32).

You don't need all five. The NO.BREAKER guide explains where to start.

K18 vs NO.BREAKER: side by side

Per ml isn't a fair test on its own. K18 is used in tiny amounts and not every wash, so a 50ml bottle lasts longer than you'd expect. It's still the pricier way in: the full-size K18 is $149, while you can start NO.BREAKER at $36.92.

Are they the same thing?

No, and we won't pretend otherwise. K18 says it works through a specific peptide. Sebastian describes NO.BREAKER as a bond-building system. Neither brand claims its product does what the other's does, and nobody has tested the two head to head, so there's no honest way to say which repairs "more". What we can tell you is what we see in the salon. Clients who use a routine every wash tend to keep using it, and that consistency is most of what makes any of these work.

Breaking or just dry? A quick check

Before you spend on any of these, work out which problem you have. Take a single wet hair from your brush and stretch it gently. If it stretches a little and springs back, the inside is mostly fine and what you're feeling is dryness on the surface. If it stretches like chewing gum, or snaps straight away, that's the breakage bond builders are made for. Short broken bits around your hairline and crown after lightening tell you the same thing. Dry hair wants moisture. Breaking hair wants a bond builder, then moisture.

Where Penetraitt fits

A lot of hair that people buy K18 for is damaged and dry rather than snapping. For that hair, Penetraitt is often the better match. The Overnight Serum ($63.32) is a leave-in that Sebastian builds on hyaluronic acid and niacinamide; 3–5 pumps through the lengths, damp or dry, and leave it in. Pair it with the Penetraitt shampoo and the weekly Rescue Repair Mask ($51.88). Hair that's breaking and rough can run NO.BREAKER and Penetraitt together. Our Penetraitt guide and damaged hair treatment guide go further.

K18 vs Olaplex

This comes up too. Olaplex No.3 is a pre-shampoo treatment you leave on for at least 10 minutes and rinse out; Olaplex says its patented active relinks broken bonds. K18 is a leave-in you apply after shampoo and don't rinse. They're built on different science and fit into the week differently. We've compared Olaplex with Sebastian in NO.BREAKER vs Olaplex.

Is K18 worth it?

For someone who wants the least routine possible and will follow the no-conditioner step exactly, it can be. If you like a full wash routine, or your hair is more dry than broken, your money goes further on NO.BREAKER or Penetraitt.

Our pick

For most bleached hair we see: NO.BREAKER, with the spray if your hair is fine and the cream if it's medium to thick, plus Penetraitt Overnight Serum when the ends feel rough. UKIYO is Wella New Zealand's No.1 Sebastian Professional retailer. If your hair is breaking fast, come and see us first. Sometimes the fix is a trim and fewer heat days. Book a consult here.

The full Sebastian range at UKIYO

If the comparison above doesn't quite fit your hair, one of the other ranges probably does. Every link goes to the collection with live prices:

• Dark Oil: smoothing and shine for frizz-prone hair
• Potion 9: leave-in conditioning and styling for dry, unruly hair
• NO.BREAKER: bond building for bleached, coloured or breaking hair
• Penetraitt: repair care for damaged, brittle lengths
• Hydre: moisture for dry, thirsty hair
• Twisted: definition for waves and curls
• Volupt: volume for fine, flat hair
• Shaper hairsprays and the rest of the Sebastian styling range
• SEBMAN: hair and beard care for men

Or browse everything from Sebastian Professional in one place.

Questions we get asked

Is Sebastian NO.BREAKER like K18?

Not exactly. K18 is a single leave-in mask built on its patented K18Peptide. NO.BREAKER is a bonding routine with a pre-shampoo crème, shampoo, mask and two leave-ins. They aim at damaged hair in different ways, so neither is a straight swap.

Is there a K18 alternative in NZ?

For bleached or breaking hair, Sebastian NO.BREAKER Treatment Spray or Leave-In Cream are the leave-ins we recommend. For hair that is damaged and dry rather than snapping, Sebastian Penetraitt Overnight Serum is often a better match.

Is K18 worth it?

If you want one small bottle and very little routine, and you will follow its no-conditioner step, it can be. The 50ml is $149 NZ RRP, so it is a pricier way in than starting NO.BREAKER at $36.92 with the pre-shampoo crème.

Which is better, K18 or Olaplex?

They work differently. Olaplex No.3 is a pre-shampoo treatment you rinse out. K18 is a leave-in you apply after shampoo. Each brand makes its own claims, and they have not been tested head to head, so choose the routine you will actually keep.

Can I use K18 with NO.BREAKER?

Follow K18's directions on the days you use it: shampoo, no conditioner, then the mask. That means skipping the NO.BREAKER mask and leave-ins on those washes. If in doubt, ask us and we'll set out a routine.

How often should I use K18?

K18 suggests every wash for the first four to six washes after a chemical service, then every three to four washes.

Does UKIYO sell K18?

No. We stock Sebastian NO.BREAKER and Penetraitt for damaged hair, along with Kérastase, Redken and Wella repair ranges.

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Everything we sell is genuine salon stock, bought through the brands' New Zealand distributors and shipped from our salon on Helwick Street in Wānaka. Free NZ shipping over $75.

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More Sebastian guides

• Dark Oil: the complete range
• Potion 9: the cult leave-in
• NO.BREAKER: bond building explained
• NO.BREAKER vs Olaplex
• Penetraitt: repair for damaged hair
• Hydre: moisture for dry hair
• Twisted: curls without the crunch
• Volupt Max for fine hair
• Hairsprays: Re-Shaper vs Zero Gravity vs Fierce
• Every Sebastian styling product
• Trilliant: heat protection with shine
• Where to buy Sebastian in NZ
• Dark Oil vs Moroccanoil Treatment

Shop the full Sebastian Professional range