Formulated for damaged hair specifically — hair that's been chemically treated (color, bleach, perms) or is regularly exposed to heat styling — rather than healthy, virgin hair that doesn't need repair. Suitable for all hair types, though people with fine hair should use a light hand since it's a leave-in serum that can weigh thin strands down if overapplied. It's a retail leave-in product simple enough for home use, though it's originally a professional Bonacure line sold through salons as well.

The case for this serum over a plain heat-protectant spray is that it does two jobs in one step: the peptide/keratin phase works on rebuilding weak spots in the hair fiber and smoothing the cuticle, while the second phase sits on top as a heat and UV shield. For hair already damaged from coloring or regular styling, that combination — internal reinforcement plus external protection — is more targeted than a standalone protectant spray.

Use on towel-dried or dry hair before styling. Pump a small amount of each phase into your palms, then rub your palms together to blend before smoothing through the hair, focusing on mid-lengths and ends. Leave in; do not rinse out. Style as usual, including with heat tools.

Pros: the two-phase design gives a lightweight conditioning phase and a heavier protective phase in one product, so no separate heat protectant is needed on top; it's a leave-in, so there's no extra rinse step; the heat protection threshold (220°C/428°F) covers most flat irons and curling irons used at home.

Cons: because both phases need to be pumped and blended by hand each time, it's a slightly fussier application than a single-phase spray serum; being leave-in and oil/silicone-based, it's not ideal for hair already prone to looking weighed-down at the roots; this specific formulation appears to be a legacy item superseded by a newer Bonacure line, so long-term availability may be limited.