A variant of PE78N system intended for the constructions of a particularly high requirements for thermal insulation. Thanks to the special inserts there can be obtained very high thermal insulation. In more insulated PE78N HI version – with closed glass chamber and insulating insert, the Uf frame heat transfer coefficient equals 0,9 W/m2K. In the most insulated (PE 78N HI+) version - with closed glass chamber and insulating insert made of aerogel, the frame heat transfer coefficient equals 0,7 W/m2K.