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The properties of metal are always going to cause a loss in your thermal boundary.

For reference, the thermal conductivity of aluminum (in watts per metre Kelvin at 25 degrees) is about 238. For something less conductive, like mineral fibre insulation, the thermal conductivity is 0.04 W/mK.

If you run into aging or damaged aluminum frames or storm windows on a building, replace them with new, more functional and efficient units.

High performance windows and doors may use metal effectively as an exterior facing, for durability and connections to flashing, while interior elements are made from more insulative materials. Manufacturers of these energy efficient units will often integrate insulation into the window and door frames strategically to eliminate thermal bridging.