What Happens if You Use K18 on Hair Extensions?
Let's Find Out!

K18 is popular! Many of our stylists and salons were asking if this new product is safe for extensions.

We asked K18 their thoughts and then we put it to the test.

We took 3 wefts that had been used in a few hand-tied trainings. They had been installed and washed several times. They weren't damaged but they were rough, dry, and dull from lack of care. They were in need of some love.

Keep in mind, our wefts are Slavic. Since Slavic wefts are not exposed to as much processing when they are made, your results may vary if you try K18 on non-Slavic hair.

We asked K18 about using their product on hand-tied wefts, click the quote mark to see what they said.
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This is an original weft before any treatment.

We started by washing all 3 wefts with Iles shampoo & conditioner and them we set 1 of them aside while we test the other two.

1 weft would be washed with Iles shampoo & conditioner while the final weft would be washed with Iles shampoo and K18.

We should note, Iles conditioner is light-weight in terms of moisture. The Iles masque (which we are not using) is designed for once-a-week use to provide deep moisture. The Iles conditioner really acts by sealing the cuticle which helps to lock moisture in. This is why it's so great on fine hair.

During our tests, we are allowing the wefts to air-dry about 80% and then finishing them under a medium temperature dryer. We will not be using any other products including heat protection for this test unless noted below during a specific wash cycle.

One important point is that K18 says, "Use a clarifying shampoo if you’re a heavy product or dry shampoo user to remove buildup and help our peptide penetrate and get where it needs to go." Frame & Thread strongly advises against the use of clarifying shampoos on hair extensions.

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Wash #1

Left Side: Iles Shampoo & Conditioner

Right Side: Iles Shampoo & K18

Hair is improved. Softer, less frizz, more shine. A little fluffy. K18 hair has more texture and volume but is slightly less manageable.

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Wash #2

Left Side: Iles Shampoo & Conditioner

Right Side: Iles Shampoo & K18

Hair is improved. Softer, less frizz, more shine. A little fluffy. Dry time is notably faster on both wefts. K18 hair has more texture and volume but is still slightly less manageable.

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Wash #2 + Flat Iron

Left Side: Iles Shampoo & Conditioner

Right Side: Iles Shampoo & K18

After a few passes in the flat iron, both wefts are smooth, soft, and greatly improved from their original condition.

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Wash #3

Left Side: Iles Shampoo & Conditioner

Right Side: Iles Shampoo & K18

Both wefts are continuing to look better. They are smooth, soft, and have more shine than they did when we started.

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Wash #4

Left Side: Iles Shampoo & Conditioner

Right Side: Iles Shampoo & K18

Both wefts are continuing to look better. They are smooth, soft, and they're starting to look like new hair.

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Wash #5 + Flat Iron

Left Side: Iles Shampoo & Conditioner

Right Side: Iles Shampoo & K18

After wash #5, we blew the hair dry and flat ironed at 380°. We're still seeing some difference in the way the hair styles. The K18 side (right) has a little more volume and is not as manageable. The K18 hair is a bit less flexible. There are more stray pieces and the ends are harder to discipline. This isn't really a styling test though so we do not yet consider this to be a concern. What we are watching for is damage during heat styling. This is where Olaplex has trouble.

Since we found that K18 does not obviously damage hair after 5 wash cycles, we will start adding in some heavy round-brushing, heat styling, and UV exposure. You don't leave your hair on a countertop when you go out of the house so we have to see how it handles some real-life use. After wash #5, we're leaving the hair outside in direct hot Florida sun for 2 days. We will then round brush and heat-style.

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Wash #6 + 2 days UV exposure + 450° curling iron without heat protection. Yes, you should avoid this but we know some people do it. They're the ones coming into the salon saying their wefts are shorter and they don't know why.

Left Side: Iles Shampoo & Conditioner

Right Side: Iles Shampoo & K18

We're at the end of the recommended initial 6-wash course of treatment for K18. They now recommend use at every 3rd or 4th wash. Iles weft is smoother and softer than the K18 weft. There is a little breakage on the K18 weft at the ends and the Iles weft is more hydrated.

What Did We Learn About K18 on Hair Extensions?

While the weft we washed & conditioned with Iles was softer, smoother and more hydrated. K18 did not appear to damage our wefts when heat tools were not used. When someone asks if K18 is safe, we're ready to say it isn't really harmful but there are a couple of very important considerations.

♡ Our hair is Slavic. Non-Slavic hair may not perform as well because it usually undergoes more processing during the coloring process.

♡ If you use heat tools, it would be best to avoid K18 on your wefts. We saw a little breakage at the ends which is common when wefts are treated with protein and then heat-styled. At the very least, use a very good heat protector, lower the temperature of your tools, and use only tools with very smooth surfaces.

♡ K18 recommends a clarifying shampoo for heavy product users and dry shampoo users. We do not. Clarifying shampoo should not be applied to hand-tied wefts. If you must clarify, perform a half-wash and only apply clarifying shampoo to your natural hair.

♡ Moisture is critical to hand-tied wefts. We experienced dryness on the K18 weft. We reached out to K18 and they told us that "clarifying the hair is a requirement and this allows their product to penetrate the hair shaft. Without clarifying, the product can sit on top of the shaft". It should be noted that their website says "our unique blend of 3 alcohols function to open up the hair cuticle so the K18Peptide can penetrate the inner most layer of hair". They also said hair should get a moisture treatment after K18.

♡ K18 works well to repair natural hair. Our educators have seen this first-hand with clients. It seems to have no benefit on extensions. Use it on your natural hair. Try to avoid getting it on your wefts but, if you occasionally do, it shouldn't hurt as long as you follow it with a moisture treatment.