Thermal blackout curtain

Thermal curtains cut overnight heat loss through glass when they’re closed and actually sealed at the edges. A pretty panel that hangs six inches off the wall is mostly décor.

Preview the criteria we used. Club has the full window test notes and hang tips.

What matters

Close fit, layered fabric or foam lining, and habits — open on sunny days, closed on cold nights. Measure energy vibes with room comfort first; bills need a longer window to prove.

• Overlap the window frame; minimize side gaps.
• Floor-length helps on radiators-under-window layouts — with fire safety in mind.
• Pair with a draft snake for the sill if needed.

Install notes from the test

• Close gaps at the sides — light leaks are heat leaks.
• Floor-length beats short panels for draft control.
• Layer with existing sheers if you want daytime light without full open.

Habits seal the deal

The best thermal curtain fails open all day on a zero-degree afternoon while the furnace runs. Pair fabric with a simple open/close habit tied to sunrise and bedtime.

A curtain that actually moves the thermometer is insulation you can hang in an hour.

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Mounting matters

A thermal curtain that hangs short of the sill or floats off the wall leaks air around the edges. Close the side gaps, use a proper rod, and layer with existing sheers if needed. We measured glass-adjacent temperatures with and without the curtain at night.

Member version includes the temperature deltas and the product traits that correlated with real gains.