Window Systems 70T The 70T window system model provides flexibility in design as well as very good heat and sound insulation. The 70 T model, which is quite suitable for use by architects, is very much preferred. 70TH The 70T window system model provides flexibility in design as well as very good heat and sound insulation. The 70 T model, which is quite suitable for use by architects, is very much preferred. 84T The 84T window system model provides flexibility in design as well as very good heat and sound insulation.