The smoothness. Not only does the serum repair hair, but also protects it, so damage doesn't happen in the first place. It has nice smell and texture. My hair loved it. Already on my second bottle of it.

I love it! The texture and it goes well with my other products of Olaplex. My hair is finally becoming less frizzy.

I use this product for a few months. My hair feels so much healthier with this hair serum. I'd recommend it!! 

The new addition number 9 works well for me as a finish and final step in my routine. I’ve not noticed improvement to my hair in the long run with this product, however it gives a nice glossy finish after styling or curling my hair and works better than an oil for me. 

I’m a huge fan of Olaplex, a brand that has made a huge difference to my hair. I will do a full Olaplex treatment routine (0, 3,4 and 5) almost every week and I also use No. 6 and 7 regularly for styling. I like Olaplex 9 because of the heat protection (the oil has heat protection, but I don’t think a few drops will provide adequate protection for proper heat styling). I use No.9 as the first styling step in my haircare routine, as a heat protectant. I don’t feel like I get many additional benefits from this product especially because I’m already using other Olapex products, but it does improve shine and smoothness if I use it with other non-Olaplex shampoos and conditioners. Since I always use a heat protectant before heat styling, I will continue to purchase because I trust this brand.