K18 is fast becoming my go-to brand for effective hair repair formulas, so I jumped at the chance to try its new heatbounce heat protection spray (£48, Spacenk.com). As the eighth product in its roster, the brand now has an all encompassing collection that covers all your needs, including cleansing, conditioning, smoothing, volumising, repairing and protecting.
First, the molecular repair leave-in conditioner (£30, Spacenk.com) convinced loyal Olaplex users to make the switch to K18. Then came the airwash dry shampoo (Spacenk.com), which had even sceptical TikTokers defending its £48 price tag. And now, I’m left wondering – could the brand’s latest release really be worth yet another £48?
As a beauty writer who tests haircare products day on the daily, I’m not an easy test subject to win over, but even I can’t deny heatbounce’s unique appeal: that its protection lasts through multiple styling sessions. Scroll on for my honest verdict after trialling with a variety of heat tools.
How I tested
Testing over the course of three weeks (with early access to the product), I used K18’s heatbounce conditioning heat protection spray on my hair in three different settings: before using my hair dryer, before using hair straighteners and before using a hair curler. I applied enough spray to adequately coat my fine-medium thickness hair (around 10 pumps), before brushing and styling as usual. During use, I paid attention to the following criteria:
- Scent: I considered whether the formula had a scent and, if so, whether it was pleasant or had staying power post-styling
- Ease of use: With such a high price tag, I wanted a small amount of the formula to go a long way, so I noted how moveable the liquid was once on the hair itself, plus the surface coverage of the mister (was it a fine, widespread mist or more of a powerful stream?)
- Conditioning benefits: The product mentions conditioning in its name, so I assessed whether or not my hair felt moisturised or dry after use.
- Protection effectiveness: When my hair suffers heat damage, it leaves a bitter odor in the damage’s wake, which was convenient when testing a heat protector. In addition to this unpleasant scent, I inspected my hair post-drying, curling and straightening for any signs of brittleness and notable split ends. However, the latter was more difficult to associate with this particular product, rather than any prior heat damage.
Why you can trust IndyBest reviews
Lucy Smith has been reviewing haircare products for IndyBest since July 2024 and is well-versed on the best products for all hair types and conditions, be they straight, curly or dyed. Specifically, she’s headed up The Independent’s guides to the best hair brushes, the best leave-in conditioners and the best shampoos and conditioners, not to mention speaking with expert hairdressers and trichologists. As someone who curls her hair two to three times a week, she was well placed to test K18’s latest heat protectant and had a number of tools at her disposal to do so.
K18 hair heatbounce conditioning heat protectant
Hair types: All
Effect: Conditions, protects, detangles
Heat protection: Up to 232C
Fragrance: Yes
Vegan and cruelty-free: Yes, both
Why we love it
- Withstands multiple styling sessions after just one application
- Pleasant citrus scent
- Smoothing
- Hair remains soft after styling
Take note
- Quite wet, so needs time to dry before styling curls
- Easy to overdo it and weigh down hair
- Expensive and small quantity
Using a trademarked and patented component that K18 calls ‘resilicore’, the heatbounce protectant spray works within the strands and reacts to any heat the hair is exposed to. By comparison, traditional heat protectants sit on the surface of the hair and act as a physical barrier to heat damage. As the brand puts it: “It delivers intelligent heat protection that penetrates deep into the hair fibre – reinforcing inner bonds and preserving strength by dynamically responding to heat.”
Aside from the ‘resilicore’, the formula boasts peptides, vitamin E, argan oil, strengthening proteins and rice to nourish, plus rosemary and lactic acid to boost scalp health. So there’s certainly enough ingredients and benefits to justify its £48 price. That being said, the product doesn’t have size on its side, with only 188ml of liquid.
Physically, the heat protectant has a double cream-like texture with enough slip and moisture to spread across multiple sections of hair, and its citrus scent is refreshing.
If you’ve tried the airwash dry shampoo, you’ll be familiar with the slightly chalky residue left behind once the hair dries. The heatbounce formula is similar and, if you’re one to finger comb your hair, this does impede that process. However, it definitely helped with detangling my knot-prone strands when wet.
I found the heat protection element to be effective after both blow-drying and styling with hot plates, and my hair was left smoothed and soft without any brittleness. If you're applying it to dry hair, make sure to let it fully dry before styling—especially if you're aiming for long-lasting curls and bounce. I found this out the hard way when a few of my curls sizzled as soon as they touched the tong. That said, even without allowing the protector to dry, I didn’t notice any visible breakage from the wet-to-dry approach (though I wouldn’t recommend it).
Aside from its obvious benefits, the best part about this product is how low-maintenance it makes the styling process. If you’re taking your hair from soaking wet to styled – whether that’s curls, waves, or poker-straight – the K18 Heat Bounce Spray doesn’t need to be reapplied between blow-drying and heat styling. Similarly, if you’ve used it for a blow-dry, you’ll still get UV and environmental protection during any follow-up with hot tools. When I put this to the test – taking my hair from just-washed to fully straightened – I could tell it was still protected, as I didn’t experience the usual mid-strand breakage I get when skipping heat protection.
If I had one tip for anyone thinking of investing, it would be to go easy on the application. As mentioned, the spray has a slippery texture, so just a few spritzes go a long way – allowing you to cover a large section of hair while making the bottle last even longer.
Buy now £48.00, Spacenk.com
Is K18 heatbounce heat protection spray worth it?
As much as I’d love to say you don’t need to spend £48 on a heat protection spray, I have to give credit where it’s due – K18 has nailed it with this one. The heatbounce formula combines strengthening and protection in a weightless serum-like spray that kept my curls bouncy and my straight styles smooth, without weighing anything down. That said, it can feel a bit heavy if overapplied, and it’s not as nourishing as the K18 leave-in. Still, if you’re already using the brand’s mask in place of a traditional conditioner, heatbounce is a natural next step. And if you regularly go from wet hair to fully styled in one session, the lasting protection – even through blow-drying – is hard to beat.
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