Dull, frazzled lengths? A bond repair hair treatment is the answer. From Olaplex to K18, Living Proof to Redken, we put the best bond builders to the test for strong, glossy locks

The bond hair repair treatment is having a moment. But until Olaplex exploded onto the haircare scene back in 2014, you probably didn't know what a 'hair bond' was. Now we're spoilt for choice when it comes to finding the best deep, restorative hair bond repair treatment, thanks to a string of high-tech new launches from the likes of K18, Redken and Living Proof, which are taking bond repair to new levels, with prevention as well as cure. The latest buzz is surrounding Epres, a new bond repair haircare brand just launched by Eric Pressly, the inventor and scientist behind Olaplex - though it's currently only shipping to the US. Watch this space.

What are hair bonds and why do they break?

Back to basics - what are hair bonds? Hair is largely made of keratin, and like any protein, it's composed of amino acids, which are joined together by bonds. "Think of hair bonds as the scaffolding that runs right through the middle of the hair shaft and makes up the strength and elasticity of your hair," says Michael Shaun Corby, global creative director of Living Proof. "These bonds are connected in different ways, some horizontally, some vertically."

There are three main types of bonds: hydrogen bonds, ionic (or salt) bonds and disulphide (covalent bonds - still with us?) and they all behave differently when your hair is exposed to humidity, heat and stress. The first two break quite easily with moisture and then reform - the reason why your hair shape looks different (say, less curly) when it's wet than when it's dry. It's also the reason why your hair becomes more fragile when it's wet and many stylists recommend wrapping it in the best hair towel you can get your hands on and gently squeezing rather than rubbing it after you've washed it. The last ones (disulphide) break permanently under stress from factors such as heat, colouring or tugging.

"Hydrogen bonds are the weakest type of bond, they break down easily with humidity," says Corby. This is why your hair loses its style or goes frizzy when it's humid and a humidity-proofing hair product is your friend. They reform again when the hair is dry, which is how you can 'set' your hair with heat in your chosen style. "They're like the little worker bees holding everything together and there are lots of them," he says.

"Ionic [or salt] bonds are stronger but they still break down when the hair is completely wet. Both hydrogen and ionic bonds break and reform all the time."

Lastly, the covalent bonds (disulfide bonds are a type of covalent bond), he says, "are the strongest, are more brittle and don't naturally repair themselves." These are the ones that when they break, make your hair look frazzled, dry and hard to style. You need a bond-building treatment to repair them - some newer bond builders such as Living Proof Triple Bond Repair also work to strengthen these to help prevent them from breaking in the first place. Others, such as Olaplex, work to repair broken bonds, making it suitable for hair that has already been damaged rather than as a protective step.

Who needs a bond repair treatment?

Everything from colouring to heat styling to brushing and environmental aggressors such as pollution can cause disulphide bonds to break, so if your hair looks a little lacklustre, dry or extra frizzy, chances are you’ve got some damaged hair bonds. Unlike conditioners that coat and hydrate strands, bond repair hair treatments work to heal and strengthen the shaft from within, working on one or more types of bonds, depending on your product.

You can’t actually see broken bonds, as they occur in the inner layer of the hair, stylist and colour expert  Samantha Cusick, whose eponymous hair salons are in London's Notting Hill and Fitzrovia tells us that dry, damaged or chemically-treated hair more than likely has bonds that have been broken, showing themselves as coarse, dry, frizzy hair that breaks easily.

How often should I use a hair bond repair treatment?

This depends on the condition of your hair and the product instructions.  “If you have hair that is weak and prone to breakage, or you do a lot of heat styling, you should try to use a bond-maintaining shampoo and conditioner every time you wash, plus a deeper reparative treatment once a week,” says Cusick. “If your hair is generally healthy and you just want to make sure it stays that way, weekly bond-building masks are great for this.”

Be careful not to over-use a hair bond repair treatment

While home bond builders are a boon, especially for repairing bleach- and heat-damaged disulphide bonds, they can be used incorrectly or even needlessly, so top stylists tell us. Colourist and co-owner of Four London Charlie Double offers both K18 and Olaplex as basin treatments to her clients and says that while Olaplex has its place for truly damaged hair, she finds that many clients are over-using the at-home treatment, often when their hair isn't damaged enough to need it. "I can tell because their hair becomes very brittle. For those people, I prefer K18,” she says.

Meanwhile, stylist Adam Reed, founder of Arkive Haircare prefers an approach that looks after the hair so it doesn’t become damaged enough to need a pricey disulphide bond builder. “You only need one if you’ve broken the bonds in your hair by using bleach,” he says. “You shouldn’t encourage your hair to need the bonds to be fixed - don’t let it get that bad!”

However, he does rate Living Proof's new Triple Bond Repair and K18 as smoothing and styling treatments.

How long do bond repair hair treatments take to work?

The good news is they get to work right away. Each time you use bond-repairing hair care, the condition of your hair improves, says Redken educator Jack Cunningham-Rose.

Each product has its own treatment time. Olaplex at-home haircare products typically take ten minutes for the bond-building tech to work its magic, with others such as K18 it's just four. Living Proof's new Triple Bond Complex requires ten minutes after your conditioner step to work and then needs to be activated by a shot of minimum 60C heat to activate the healing technology.

We've tested some of the best bond repair hair treatments for coloured and heat-damaged hair (and, by the way, our locks have never looked or felt stronger).

Best for all hair types (even hair that isn't badly damaged): Living Proof Triple Bond Complex 45ml, £42

The newest bond repair product to launch, Living Proof's Triple Bond Complex contains technology that the brand claims can strengthen, reform and even create brand new bonds of all three types, making your hair up to eight times stronger (they've stress-tested it in the lab against their biggest competitors, which snapped sooner). "Other bond-builders can repair covalent bonds, but it usually requires them to be damaged in the first place, whereas we don't. That's why we call it 'future-proofing your hair,'" Corby says.

Most bond-building products repair bonds in either one direction (vertical or horizontal), he says, while Triple Bond Complex repairs in all directions. The result is hair that is stronger, softer, smoother and more resilient to damage, they say.

Apply two pumps (and up to six) to damp hair after your conditioner step, wait ten minutes, then dry your hair as normal. The brand notes that the best results are achieved through activating the treatment with 60C heat. A simple quick shot of low heat is fine, so if you normally air dry blast it when the hair is wet and leave it to drip dry as normal, that's fine, too.

After one treatment, one GTG writer noticed their hair felt and looked thicker and stronger, and their beach waves lasted well into the next day (a rarity for some of us). Having a longer-lasting style is another benefit the brand says customers notice because the complex prevents the easily broken hydrogen and ionic bonds from breaking as quickly.

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Best for convenience: K18 Leave-in Molecular Repair Hair Mask 50ml, £55

When K18 launched in the UK earlier this year, it was immediately dubbed 'the new Olaplex' by beauty editors. K18's bond-repairing treatment features a patented peptide which mimics keratin chains found in the hair shaft (which are the vertical lengths of the hair shaft ladder) and repairs horizontal disulfide bonds along the way. The brand inspected thousands of sequences of amino acids in the hair to find the winning formula, which the brand likens to the "missing piece of the puzzle."

This is possibly the most straightforward bond repair hair treatment we've used. Simply shampoo your hair and gently towel dry, no need for conditioner. Apply two small pumps - a little goes a long way - then leave on for four minutes and you're good to go, whether that's following with heat styling or leaving your hair to air dry.

For one GTG writer, this has replaced conditioner - less time in the shower means more time in bed in the morning! Her hair appears fuller, ends less split and, surprisingly for a leave-in product, it leaves no greasy residue. Both K18 and Living Proof's treatments are travel-friendly sizes, too.

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Redken launched its best-selling (and now TikTok famous) Acidic Bonding line last year, with a shampoo, conditioner and leave-in treatment, all designed to target weakened bonds of processed hair. Now, it has just followed up with the line's Intensive Pre-Treatment, which you could say is a rival to Olaplex's now-cult No.3 Hair Perfector.

The entire range contains its own Bonding Care Complex, plus citric acid, an alpha hydroxy acid (AHA), which helps reinforce weakened bonds - and this pre-treatment features the highest concentration of any of the products in the range. If you like a nice-smelling shampoo, then this is for you. The entire range smells like salon haircare and our tester found it made her hair smoother and bouncier after one use, making it feel more elastic in a good way. When used in tandem with the shampoo and conditioner, it was found to improve breakage reduction for up to twice as strong hair, according to the brand.

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Best for damaged hair: Olaplex No.8 Bond Intense Moisture Mask, £26

You're probably already aware of the now cult Olaplex No.3 pre-treatment, the OG hair bond repair treatment, but Olaplex No.8 Bond Intense Moisture Mask is fast converting beauty editors. Our tester applied this the first time she washed her hair post-bleach and was impressed by how easily it soothed her distressed hair, which normally tangles like a bird's nest post-colour. It works to reinforce fragile bonds to make the hair look smooth and shiny, with avocado and hemp oil to nourish. You need to leave it on for ten minutes for it to get to work, so not one to use if you’re in a rush. Samantha suggests using this to maintain freshly coloured hair from home, or to top up hair that’s had an Olaplex treatment in-salon. It’s a fairly thick mask and it soothes the hair cuticle for that smoothed look, but it doesn’t feel heavy on the hair.

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Best budget hair bond treatment:  The Inkey List PCA Bond Repair Hair Treatment, £12.99

Just like all of  The Inkey List’s hair care, this is pleasingly affordable and just as high performing as you’d expect from the brand. It's preventative as well as repairing. PCA stands for pyrrolidone carboxylic acid a very small silicone  - the brand says. don't panic, it's non-irritating. It’s a lightweight leave-in mist that helps to strengthen and rebuild all three types of bonds, improving shine and helping prevent split ends. You need about ten sprays if you have shoulder-length hair, like our tester, and while the nozzle is a bit stiff and difficult to use, it’s well worth it in terms of manageability and smoothness.

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Best quick rinse-out hair bond repair treatment:  Amika The Kure Multi-Task Repair Treatment, £23

If you love hair waters, this light treatment will be right up your street. It has the texture of slightly thick water and glides through hair with that unmistakable fresh Amika scent. You use it after shampoo and conditioner and rinse it out after one minute, though if your hair is extra damaged you can leave it in to give hair an extra layer of protection. It’s made from a blend of plant butter, including mango butter extract, shea butter and borage oil and adheres to damaged areas of the hair to make them more resilient (just like hair waters do). It also includes castor oil, which is known to be a BFF to damaged hair for stronger locks.

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Best vegan and heat-protecting hair bond repair treatment:  Aveda Botanical Repair Strengthening Leave-In Treatment, £28

This took six years in the making and is designed to strengthen and repair damaged hair with plant-derived technology, working on three layers of the hair to protect it from the inside out. It’s silicone-free and sulphate free too and vegan. It has a gel-cream texture that mimics the outer layer of the hair to create a protective shield that makes the hair five times stronger but is lightweight and undetectable when you apply it. Apply to damp hair as you would a blow-dry cream and it melts in, making a sort of veil of protection, providing heat protection up to 230 degrees and UV protection too. Our tester found her hair was instantly smoothed but did find herself using a lot as it’s lightweight so you feel the need to keep smoothing it on.

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Best bond treatment for split ends:  Philip Kingsley Bond Builder Split End Remedy, £26

Split ends are a surefire way to ensure your hair never looks polished, luckily this bond builder from trichologist brand Philip Kingsley is here to save the day. It’s a light but creamy formula that you smooth through the lengths of your hair every three washes, to bond the splits back together. Obviously, the only way to banish split ends for good is to chop them off, but this minimises the appearance, working on the cuticle itself and the outer layer. It seals and strengthens weak strands without weighing them down. In independent trials, 98.6 per cent of split ends were sealed after one application. Our tester has an overly-styled and coloured fringe and this worked like magic to make it look less brittle at the ends, without looking greasy. It fuses the damaged bonds together, shrink-wrapping them for a much healthier hair look.

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