Head to Head
K18 Leave-In Mask vs Olaplex No.8
K18's leave in peptide treatment against Olaplex No.8's rinse out moisture pump: different formats, different jobs, and which one a damaged, dry routine actually needs first.
K18 Leave-In Molecular Repair Hair Mask
The leave in exception: a peptide treatment the brand publishes under molecular repair naming, used in place of conditioner, never rinsed out.
Olaplex No.8 Bond Intense Moisture Mask
The moisture pump from the bond named line: the brand's Bond Building Technology in a rinse out mask for smoothness, body and shine.
Where They Differ
Format and routine
K18 is used after shampoo with conditioner skipped, towel dried hair, one to three pumps, four minutes, no rinse. No.8 is used in the shower on clean, damp hair, left ten minutes and rinsed out. One shortens the routine, the other occupies it, and that alone settles the choice for many buyers.
What each formula is built around
K18 is organised around a single patented peptide, printed as sh-Oligopeptide-78, and the brand publishes it for damage from bleach, colour, chemical services and heat. No.8 carries the Olaplex Bond Building Technology as the line's published system, inside a formula whose stated aims are moisturising, smoothing, body and shine. Treatment system versus moisture system is the accurate summary of both labels.
Value shape
K18 is 50 ml dosed in single pumps, with the brand printing 16 to 50 treatments per bottle. No.8 is 100 ml dosed generously by the pump and finished faster on long hair. Comparing sticker tiers without comparing dose misleads in both directions; cost per wash day is the fair measure, and it is closer than the bottle sizes suggest.
The Specification, Side by Side
| Measure | K18 Leave-In Molecular Repair Hair Mask | Olaplex No.8 Bond Intense Moisture Mask |
|---|---|---|
| Size | 50 ml / 1.7 fl oz | 100 ml / 3.3 fl oz |
| Format | Leave in cream, pump bottle | Rinse out moisture mask, pump bottle |
| Key Ingredients | K18PEPTIDE (sh-Oligopeptide-78), hydrolyzed wheat protein, tocopherol | Bis-Aminopropyl Diglycol Dimaleate (the brand's Bond Building Technology, as published) |
| Use | After shampoo only, towel dry, 1 to 3 pumps, wait 4 minutes, do not rinse, as directed on the listing | Apply to clean, damp hair from mid lengths to ends, leave 10 minutes, rinse, as directed by the brand |
| Hair Type | All hair types, as printed on the listing | All hair types, as printed on the bottle |
Choose K18 Leave-In Molecular Repair Hair Mask if
- Your hair is bleached, coloured or heat styled and looks and feels damaged
- You want the shortest routine: no conditioner step, no rinse, four minutes
- Your hair is fine and heavy rinse out masks flatten it
Choose Olaplex No.8 Bond Intense Moisture Mask if
- Dryness, dullness and tangling are louder complaints than damage
- You prefer a traditional in shower mask ritual with a visible rinse out step
- You own other Olaplex steps and want the moisture piece of that system
Questions, Answered
Can K18 and No.8 be used on the same wash day?
Owners do combine treatment and moisture steps, but the published K18 protocol says to skip conditioner, and a rinse out mask before K18 works against that direction. The cleaner pattern is to alternate wash days: K18 when you wash for treatment, No.8 when you wash for moisture. If both are used in one session, follow the K18 directions last and literally.
Keep Researching
Every page in the Hair Masks edit.
- 01Hair Masks: the hubHub
- 02Best Hair Masks 2027Best of
- 03Hair Masks for Dry HairGuide
- 04Hair Masks for Damaged HairGuide
- 05Hair Mask vs Conditioner: When a Mask Earns Its PlaceGuide
- 06K18 Leave-In Molecular Repair Hair Mask ReviewReview
- 07Kerastase Chronologiste Masque Intense Regenerant ReviewReview
- 08Olaplex No.8 Bond Intense Moisture Mask ReviewReview
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