Highly insulated, MB-Slimline window system with thermal break is intended for fabrication of external structure elements such as various types of highly resistant, inward-openable windows (side-hung, hopper, tilt-and-turn windows) and fixed windows of an excellent water resistance, air tightness, and sound insulation performance. With its very small-width aluminium profiles, visible from the external side of the construction, MB-Slimline enables to fabricate casements in two variants – with visible or invisible profiles (SG) from the external side of the structure. When invisible casements are used, the appearance of openable and fixed units is almost identical. This system can also greatly replace the old-style windows, made of steel profiles and maintain a similar appearance from the outside of the construction, while significantly increasing the thermal insulation of the partition.