K18's Professional Molecular Repair Hair Mask is the second step to K18's two-step in-salon service, following the Professional Molecular Repair Hair Mist, and works as a stand-alone treatment. This leave-in mask works with all hair types and should be used before any chemical treatment, hair coloring, or even heat styling, as well as before and after toning, to keep locks strong and damage-free.K18 products use the K18Peptideu2122 to penetrate each strand and repair broken polypeptide (keratin) chains for soft, smooth, bouncy manes. This lightweight mask restores strength and elasticity to a client's preexisting damage, and it doesn't wash away.Also check out K18's Leave-in Molecular Repair Hair Mask.