Do Blackout Curtains Keep Heat Out? What You Need to Know.
When you think of blackout curtains, you probably picture a dark room free from sunlight — perfect for sleeping or watching movies. But many wonder if these curtains do more than block light. Specifically: Do blackout curtains keep heat out? Let’s dig into that.
What Are Blackout Curtains Made Of?
Blackout curtains are usually made from dense, tightly woven fabrics that prevent light from passing through. Some have an extra lining—like foam or thermal polyester—that adds insulation. This thick construction is the first clue they can affect heat transfer, not just light.
How Heat Moves Through Windows
Heat enters your home mainly through windows via:
Solar radiation: Direct sunlight warms the glass and air inside.
Conduction: Heat moves through the glass itself.
Air leaks: Gaps around window frames let hot or cold air in.
Blocking sunlight and adding insulation slows down these processes.
Blackout Curtains and Heat Blocking — What’s the Science?
Because blackout curtains block sunlight, they reduce solar radiation entering your room. Less sunlight means less direct heat warming your space.
The thick fabric and especially thermal linings provide a layer of insulation. They slow heat conduction through the glass by trapping air between the curtain and window—air is a poor heat conductor, so this helps keep heat out.
Studies and product tests show that blackout curtains with thermal linings can reduce heat gain through windows by up to 30-45%. That’s a significant amount, especially during hot summer days.
But Not All Blackout Curtains Are Equal
Fabric thickness matters: Thin blackout curtains block light but might not insulate well.
Thermal lining is a game changer: Curtains labeled “thermal” or “insulated” offer the best heat-blocking.
Proper fit is crucial: Curtains should cover the entire window plus some extra on all sides, minimizing gaps where heat can sneak in.
Installation counts: Wrapping curtains around the window frame or using track rods improves effectiveness.
What Blackout Curtains Won’t Do
Blackout curtains help, but they’re not a full replacement for:
Proper window glazing or double-pane windows
Window films designed specifically for heat reflection
Sealing leaks and drafts around windows and doors.
Tips to Maximize Heat Blocking
Close blackout curtains during the peak sun hours.
Combine curtains with blinds or shades.
Use fans or air conditioning for airflow.
Choose curtains with high-quality thermal lining.
Make sure curtains fit well, sealing edges.
Final Verdict
Do blackout curtains keep heat out? Yes, especially when they have thermal linings and are properly installed. They’re a cost-effective, stylish way to reduce heat gain through windows and improve home comfort.
While they won’t solve all your temperature problems alone, they are a strong piece of the puzzle for anyone looking to keep their home cooler in summer and warmer in winter.
