A metal-framed window with which feature(s) would be the best thermal barrier?

The best thermal barrier for a metal-framed window is achieved through the use of thermal breaks between metal components. A thermal break is an insulating material that is placed between the interior and exterior metal parts of a window frame. This design minimizes the transfer of heat and cold, making it significantly more effective than a continuous metal frame, which would allow thermal energy to pass through easily.

The presence of thermal breaks can effectively reduce heat loss in winter and heat gain in summer, improving the overall energy efficiency of the window. By interrupting the pathway of thermal conduction, thermal breaks help maintain a stable indoor temperature, contributing to better comfort and reduced heating and cooling costs.

Other features mentioned, such as single pane glass, double pane glass without argon, or low-e glass coatings, do contribute to energy efficiency but do not provide the same level of performance enhancement as thermal breaks in metal framing specifically. Single pane glass offers very poor insulation, while double pane glass without argon may still allow for some thermal bridging through the frame itself. Low-e glass coatings reflect infrared energy but don't necessarily address the conductive heat transfer through the metal frame, which is where thermal breaks come into play effectively.