The ones with fine hair like me know the struggle when you wonder whether you have to wash it or not. Because if you don't, it will look flat and sad but if you do, it will be breaking and dry. I try to push the day I wash my hair to its maximum to try and protect it with the "low-poo" method (use no shampoo or very gentle versions), but in the end I am a model and hairdressers often use (many) products on my hair and I had to find a solution for healthy but clean hair.
I found the Replumping shampoo and conditioner by Davines on Birchbox, as I was searching for a thin hair solution. As I already had the chance to try - and love - the brand, I ordered it right away wondering if it would be just another failure to find the perfect shampoo or a win decision. As you guessed it, if I am talking about it here it's because I am beyond satisfied ! It doesn't really give more volume so to speak, but the hair does feel completely healthy and sleek, a feeling I actually haven't had for a while, it looks very smooth and shiny.
There's no special way to use it, except that usually with hair conditioner I only apply it on the length of the hair, but with these I also massage the base of the hair to protect the whole thing. Of course, you'll need more styling products to achieve a desired volume, but it's important to have a healthy base before trying to style it.