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How to line curtains
Select a thermal liner if you'd like to insulate your windows.
If your windows are drafty or thin, save on your heating and cooling costs by lining the curtains with a thermal fabric. The insulation will keep heat in your room during the winter while keeping out drafts from the window.
It will also keep cool air from escaping during the summer months. Most thermal liners are made from cotton, polyester, or a blend.