argon filled windows

https://wiki-book.win/index.php/Why_a_Free_Window_Estimate_Can_Save_Time_and_Money_on_Replacement_Projects

Argon filled windows have a layer of inert argon gas between the panes, which slows heat transfer better than plain air. This helps keep your home warmer in winter and cooler in summer, while also reducing condensation and outside noise. It's a simple upgrade that makes a real difference in comfort and energy bills.