Vapor insulation of the roof

At the moment I am repairing the roof. We need to make good vapor insulation. Everyone on the Internet advises to use film, and what can you advise about it?

That's right, it's better to do everything as correctly and efficiently as possible. I decided to order a three-layer translucent reinforced vapor insulation film "TECHNONICOL ALFA-BARRIER 3.0" - https://technonicol.in/ . Performs its functions perfectly.