A window looks like a sheet of glass in a frame, but a modern insulated glazing unit is a precision thermal device: stacked panes, a sealed cavity of heavy inert gas, and a coating of sputtered silver a few atoms thick that reflects heat while passing light. The layered construction, what low-E and emissivity actually mean, how to read an NFRC label honestly, and why triple pane is sometimes a trap.
Low-E
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How a Modern Window Is Engineered