Find manufacturer of this butyl rubber foil (pond liner) in europe (or close to europe)

Dear all, we are looking for the manufacturer of this "butyl rubber foil", it is also known as (pond liner). This foil is used to put it under new buildings to protect the building agains the radiactive gas RADON (and also water ... ) You can find a detailed description of this foil in the attachment (sorry, it is only in german available) The diffusion resistance factor is the most important factor for us and it has to be 300.000 This means, it is 100 % steam-tight and radon tight. Material Specification Hardness ° IRH 65 ± 5 Tensile strength MPa min 8.5 Elongation % min 350 Tear strength kN / m min 20 Foldability at low temperatures ° C max -40 Water vapor permeability μ 300,000 Thickness mm 1.2 The manufacturer of this foil should be located in germany or at least in europe (because of the heavy weight - transport costs)