Thermopane windows can be explained as two pieces of glass joined together with an insulation gap between them.
An energy efficient glazing method is used in thermopane windows where two pieces of glass are attached to each other with an aluminium spacer bar. The spacer bar is filled with desiccant which removes any moisture from the space between the two pieces of glass. The Spacer Bar has a Primary Moisture barrier (Butyl) and a Secondary Barrier. The air between the two pieces of glass is replaced with an inert gas IE: Argon Blend, this further reduces the thermal conductivity of the Panel.
Thermopane windows are used increasingly to reduce heat / cold loss in glazing systems. It also has significant benefits from reduced noise transmission.