PHS Apollo 2 Vapour Control has an optimum fixed vapour resistance level of Sd 27m. This allows for an ideal level of vapour control by preventing diffusion of internal vapour into the building envelope back in winter and allowing diffusion in summer. This prevents a build-up of condensed water vapour within the building envelope, that facilitates mildew growth and constructional damage. The CE sign according to DIN EN 13984 gives the necessary assurance for the quality of the product.