The filler is designed for regular home use, and the effect — hair that feels denser, smoother and more elastic — builds up with repeated applications. There is no single fixed schedule, because it depends on how damaged your hair is.
As a starting point, apply it every time you wash your hair, or every second wash, and then adjust. Hair that has been bleached, highlighted, permed or regularly heat-styled usually needs more frequent use than hair that is only slightly dry. If your hair starts to feel stiff, brittle or overloaded, simply reduce the frequency — this is a common sign that the hair has had enough protein and needs a break.
You can combine the filler with your usual products. The product is intended to be used together with a gentle shampoo and a nourishing mask once a week. The filler goes on clean, towel-dried hair, so it comes after your shampoo and mask. Because it is leave-in, it can replace a separate leave-in conditioner or styling cream, but you can also layer a styling product on top if you need extra hold or heat protection.
One practical note: apply it to the lengths and ends, not to the scalp, to keep the roots light. If you have fine hair, start with a small amount and add more only if the hair still feels dry or rough.