High thermal insulating mullion and transom curtain wall system most often used in energy-efficient construction. Designed special thermal insert, which fills the space between the glass, both by its shape and properties improves the parameters of the entire structure. The structure of the plastic allows proper drainage of the transom; its shape allows for easy installation, which takes place after the glazing is installed. Thermal properties make it possible to achieve a heat transfer coefficient Ucw from 0.6 W/m2K (for fillings 48 mm thick).