What each one is sold to do
Hair is made of keratin, a protein made stronger and stiffer by disulfide bonds between its cysteine; human hair is about 14% cysteine. A perm works by breaking those bonds and closing them again around a rod, and chemical straightening and relaxing use the same process.
Protein treatments are sold to strengthen hair with protein: hydrolyzed wheat, rice or keratin protein, collagen or amino acids. Bond-building treatments are sold as reconnecting the bonds inside the strand that chemical services break. Both are the makers’ claims, not results we measured, and no label says how much of anything a product holds.
Nine treatments’ directions, side by side
The two bond treatments come first, then the protein treatments from the shortest time on the hair to the longest. Every line is from the maker’s own directions; where a maker gives no figure, the table says so.
Where each treatment goes, and for how long
| Treatment | Where it goes | Rinse or leave in | Time | How often, the maker says |
|---|---|---|---|---|
| K18 Leave-In Molecular Repair Hair Mask bond-building; not in our catalogue | After shampoo, towel-dried, no conditioner first; one to three pumps from the ends up | Stays in | Four minutes before you comb or add another product | Four to six washes in a row after a salon service, then as needed |
| Curlsmith Bond Curl Rehab Salve sold as bond-building and protein-rich; not in our catalogue | On wet hair before shampoo, roots to ends, then detangle | Rinse out, then shampoo and condition | 15, 20 or 30 minutes, for Curlsmith’s low, medium or high porosity | Every 4–5, 3–4 or 2–3 wash days, by the same porosity |
| ApHogee Keratin 2 Minute Reconstructor protein | After shampoo, half an ounce through the hair and into the scalp | Rinse out | 2 minutes under a warm towel or plastic cap; 5 for what ApHogee calls extreme cases | Not stated |
| Redken Extreme CAT Protein Reconstructing Treatment protein | After Redken Extreme Shampoo: spray evenly and lather | Rinse out | 3 to 5 minutes | One to three times a week |
| Curl Junkie Repair Me! Reconstructive Hair Treatment protein | On wet hair, through the lengths with fingers or a wide-tooth comb | Rinse out | 5 to 10 minutes; a plastic cap or heat for a deeper treatment | Once a month, or as needed |
| SheaMoisture Manuka Honey & Yogurt Hydrate + Repair Protein-Strong Treatment protein | A quarter-sized amount, roots to ends; it can also go on before you wash | Rinse out | 10 to 15 minutes | Not stated |
| Briogeo Don’t Despair, Repair! MegaStrength+ Strengthening Treatment protein | After shampoo, on damp hair with the water wrung out | Rinse out, then Briogeo’s Deep Conditioning Mask | At least 10 minutes, or longer, or overnight | Weekly, then every other week after several treatments |
| Cécred Reconstructing Treatment Mask protein | After shampoo and detangling, on wet hair in sections | Rinse out, then a Cécred conditioner | Up to 20 minutes; a plastic cap and heat for best results | Before conditioning, or whenever hair needs repair |
| ApHogee Two-Step Protein Treatment protein | After ApHogee’s shampoo, towel-blotted; saturate and comb through | Dried on, uncovered, under a hooded dryer or a hand dryer, then rinsed; ApHogee’s moisturizer follows for 2 minutes | Until it dries hard; don’t comb or brush it while it’s hard | Every four to six weeks |
Where the two overlap
The names on the bottle don’t sort products as neatly as the two categories suggest. Curlsmith sells Bond Curl as a bond treatment and as protein-rich. OLAPLEX names a whole line after bonds, yet lists its No.5 conditioner, No.7 oil and No.9 serum as free of protein, while its No.4 Bond Maintenance Shampoo lists one protein, Hydrolyzed Vegetable Protein PG-Propyl Silanetriol.
So read the label, not the category. If you’re pausing protein, the ingredient checker shows every protein name on a pasted label, and the product finder can leave protein out of every step. We don’t hold K18’s full ingredient list, so we can’t say whether it names a protein.
What the research shows, and what it doesn’t
One laboratory study shows why “protein only coats the outside” is too simple. Researchers relaxed very curly hair with a sodium hydroxide treatment, then applied keratin peptides of three sizes. The two smaller sizes went deep into the hair’s cortex; the largest stayed mostly on the surface. The mid-sized and large peptides made the fibres stiffer and reduced breakage at both 20% and 80% humidity.
That study tested peptides on freshly relaxed hair in a lab, not any treatment on this page, so it can’t tell you which product works or rank them. No study we read compares bond builders with protein treatments on curly hair.
Using both on the same wash day
None of these makers says how to combine its treatment with another brand’s. Their own directions put them in different places: Bond Curl before shampoo, K18 after shampoo and before any conditioner, most protein treatments after shampoo and before a conditioner or mask. If you try both, change one thing per wash day, so you can tell which one your hair is answering.
K18 gives its dose in pumps and doesn’t say how much a pump holds, so we can’t work out its cost per use the way our cost tool does for products sold by volume.
What this comparison doesn’t claim
We haven’t used these treatments; we compare what their makers publish. This isn’t a ranking, and a word such as “repair” or “strengthen” is the maker’s, not a result we checked. OLAPLEX No.3 Hair Perfector isn’t here: its US product page didn’t open when we read the makers’ directions in October 2026, and its older directions differ, so we haven’t guessed them.
Questions before your next wash
Is OLAPLEX a protein treatment?
Not by OLAPLEX’s own lists. It says its No.5 Bond Maintenance Conditioner, No.7 Bonding Oil and No.9 Bond Protector serum are free of protein. Its No.4 Bond Maintenance Shampoo does list one protein, Hydrolyzed Vegetable Protein PG-Propyl Silanetriol.
Is K18 a protein treatment?
K18 sells its mask as a molecular repair treatment that stays in, not as a protein treatment. We don’t hold its full ingredient list, so we can’t say whether the label names a protein.
How long do you leave a bond builder on?
It depends on the product. K18 stays in: wait four minutes before you comb or add anything. Curlsmith’s Bond Curl goes on before shampoo for 15, 20 or 30 minutes, the times Curlsmith gives for low, medium and high porosity, then rinses out.
Can a bond builder replace my conditioner?
Not Curlsmith’s: it says to shampoo and condition after Bond Curl. K18 says to skip conditioner before its mask and that conditioner or stylers can go on once its four minutes are up, so by its directions conditioner afterwards is optional.
Updated · The sources for this guide are on our Sources page. Report a changed detail.