Beauty This Hailey Bieber-Approved Mask Gives Shoppers Back Their 16-Year-Old Hair “To say I was transformed and humbled is an understatement.” By Rachel Nussbaum Rachel Nussbaum Instagram Twitter Rachel is a journalist, writer, and editor who specializes in the beauty and wellness industry, writing about the best, safest products the industry has to offer for InStyle, Byrdie, and Shape. InStyle's editorial guidelines Published on April 13, 2022 @ 08:00PM Pin Share Tweet Email We independently research, test, review, and recommend the best products—learn more about our process. If you buy something through our links, we may earn a commission. Photo: Getty Images Time and again, Hailey Bieber has proven her beauty chops. Her upcoming skincare line is just the tip of the iceberg: Bieber frequently posts about her beauty favorites on social media, and welcomes fellow models and celebrities into her bathroom on YouTube for skincare-centric chats. And considering the rapid-fire hair color switches that accompany model life, it makes sense her strengthening hair secret is shopper-worshiped, too. "My favorite hair product right now is called K18," Bieber told Refinery29 last year. "It's so good; I use that all over my hair every time I get out of the shower." InStyle's own pros have seen just as eye-opening results from the K18 Leave-In Molecular Repair Hair Mask: Beauty editor Erin Lukas said the soft, shiny results drew an audible "wow" from her, and earned it the title "instant gratification" in a tube. Where most hair-repairing treatments focus on rebuilding bonds with protein, K18 takes a different approach with peptides that undo the effects of chemical treatments and heat styling, which improves hair's elasticity and durability (peptides, man). It's so powerful that even people with "dry, colored, post-menopausal hair" said that it gives them "noticeably shinier" and more healthy-looking hair with a single use. Courtesy Shop now: $15–$80; amazon.com One person whose hair turned brittle after getting COVID-19 said it also helped their strands make a "miraculous recovery," and another reviewer confirmed the hype is deserved. "To say I was transformed and humbled is an understatement," they wrote of the newly soft, shiny, and hydrated hair they witnessed within three washes. "Frankly, it hasn't looked like this since I was 16…four decades ago." I personally was lucky enough to try the leave-on mask when it launched in 2020, and found it remarkable how shiny and smooth my 3B curls looked after using it for a blowout. But even people who used it on their bleached curls and wore their natural texture were impressed with the "defined, springy" results. And as a last 65-year-old wrote, it left their "thin, platinum hair" feeling strong and hefty without any residue — great things across the board. If you'd like to try Hailey Bieber's hair secret for yourself, the full-size K18 Leave-In Molecular Repair Hair Mask goes for $80 at Amazon, or you can try a smaller size for $15.