The subject of the invention is an electrically controllable device having variable optical and/or energy properties of the electrochromic type, which comprises a functional film consisting of a layer or a stack of layers which is placed between two external substrates which meet the following criteria: at least one is essentially transparent; at least one is based on one (or more) film(s) based on one or more polymers; each of them is a water vapor barrier, with a water vapor permeability of at most 1 g/m2/24 h, especially at most 0.1 g/m2/24 h.