By mid-July, a sunny window can turn one corner of your home into the hottest seat in the house. The good news is that the right window treatment helps a lot. Thermal curtains are one of the simplest ways to stop heat at the glass, lower the load on your air conditioner, and keep rooms comfortable without cranking the thermostat.

Quick Answer

To keep your home cooler this summer:

• Close your curtains during the day on any window getting direct sun.
• Choose thermal or blackout curtains with a light-colored backing.
• Start with your south- and west-facing windows, where the sun hits hardest.

Together, these three steps can noticeably reduce the heat coming through your glass.

How Much Heat Comes Through Your Windows

Windows are the weak spot in a cool home. According to the U.S. Department of Energy, heat gain and heat loss through windows account for 25% to 30% of the energy your home uses for heating and cooling.

In summer, sunlight passes through the glass and warms everything it touches. That warmth then radiates back into the room, long after the sun has moved on.

Not every window contributes equally. The direction a window faces decides how much sun it takes in during the hottest hours.

Window direction	Sun exposure in summer	Priority for heat blocking
West-facing	Intense afternoon and evening sun	Highest
South-facing	Strong midday sun	High
East-facing	Morning sun, cooler by afternoon	Medium
North-facing	Little direct sun	Low

Why Blackout Is Not the Same as Thermal

A blackout curtain is built to block light. A thermal curtain is built to slow heat. They overlap, but they are not identical.

Many blackout panels do reduce heat, because the dense fabric also resists heat transfer. But a curtain made specifically for insulation usually adds an extra layer designed to hold temperature in place. When your goal is a cooler room, look for the heat-blocking feature, not only the dark color.

The Best Curtains for Summer Heat: Thermal, Blackout, or Linen

Each fabric type handles heat differently. Here is how the main options compare when the goal is a cooler room.

Type	Heat blocking	Light control	Airflow / feel	Best for
Thermal insulated	Strongest	Medium to high	Heavier, structured	Bedrooms, sun-facing rooms
Blackout	Strong	Full darkness	Dense, solid	Bedrooms, media rooms
Linen	Light	Soft, filtered	Breezy, airy	Shaded rooms, soft daylight

Do Blackout Curtains Keep Heat Out?

Yes, to a degree. Blackout fabric is tightly woven and often layered, so it slows the heat that would otherwise pour through the glass. It also stops the direct sunlight that heats surfaces inside the room.

For full insulation, a thermal-lined panel does more. But a quality blackout curtain still makes a clear difference on a hot afternoon.

Thermal Curtains vs Blackout Curtains

Pick thermal curtains when comfort and energy savings matter most, since the insulating layer is designed to hold temperature steady year-round. Pick blackout curtains when total darkness is the priority, such as a nursery or a room for daytime sleepers.

Plenty of panels do both jobs at once, giving you darkness and heat resistance in a single curtain.

Where Shades Fit In

Cellular shades, sometimes called honeycomb shades, add insulation right at the window. Their pleated pockets trap air, which slows the heat moving through. They pair well with curtains for rooms that take heavy sun, and they suit windows where a slim, tailored look works better than full drapery.

The Color and Lining Choices That Make the Biggest Difference

Two small decisions change how well your curtains perform: the color and the backing.

Best Curtain Color for Blocking Heat

Light colors reflect sunlight, while dark colors absorb it. A pale curtain facing outward bounces more of the sun's energy back before it becomes heat.

If you love a deep, dark shade for the look, you can still get strong performance by choosing a panel with a light or reflective backing.

The Role of the Lining

The lining does much of the quiet work. The sun-facing side is what meets the heat first, so a light-colored or reflective backing helps push that energy away before it builds up inside.

This matters because the heat load is real. The U.S. Department of Energy notes that during cooling season, about 76% of the sunlight hitting a standard double-pane window enters the room as heat. A reflective lining gives you the rich front color you want while keeping that sun-facing side working to block it.

Which Windows to Prioritize First

You do not need to treat every window at once. Start where the sun hits hardest.

1. West-facing windows first. They take the harsh late-day sun when your home is already warm.
2. South-facing windows next. They carry strong, steady light through the middle of the day.
3. East-facing windows after that. Morning sun is real but fades by afternoon.
4. North-facing windows last. They rarely get direct sun, so they need the least help.

Treating your two or three hottest windows often delivers most of the comfort you are after.

How to Get the Most Out of What You Already Have

You can boost the curtains already hanging in your home with a few simple moves.

• Add a thermal or blackout lining. A separate lining layer attached behind an existing panel raises its heat resistance without replacing the curtain you like.
• Close them at the right time. During summer days, keep curtains closed on any window getting direct sun, then open them in the cooler evening to let warm air escape.
• Hang them close to the glass and let them reach the floor. The tighter the panel sits against the window and the more fully it covers it, the less heat sneaks past the edges.
• Layer for extra protection. A sheer for daytime privacy plus a heavier panel for sun control gives you flexibility through the day.

These habits cost nothing and make your existing curtains work harder all season.

Stay Cool With Joydeco

A few smart choices at your windows keep your home comfortable and ease the strain on your AC all summer.

If you are ready for an upgrade, Joydeco's custom thermal insulated curtains and blackout curtains are made to fit your exact windows, with light-friendly linings that block heat where it starts. Pick the fabric, color, and size, and dress your hottest windows for the season ahead.

FAQs

Q1: Do curtains actually keep heat out in summer?

Yes. Curtains block direct sunlight and slow the heat moving through the glass. In cooling season about 76% of the sunlight hitting a standard double-pane window turns into heat indoors, and closed window coverings help reduce that gain.

Q2: What color curtains are best for blocking heat?

Light colors reflect the most sunlight and stay coolest. If you prefer a darker front for style, choose a panel with a light or reflective backing so the sun-facing side still pushes heat away.

Q3: Are thermal curtains or blackout curtains better for summer?

Thermal curtains are built to slow heat and hold room temperature steady, which makes them the stronger choice for cooling. Blackout curtains also block plenty of heat and are ideal when you want full darkness too. Many panels combine both.

Q4: Should curtains be open or closed in summer to keep the house cool?

Keep them closed during the day on windows getting direct sun to stop heat from building up. Open them in the cooler evening so trapped warm air can clear out.

Q5: Can you add thermal lining to curtains you already own?

Yes. A separate thermal or blackout lining can be attached behind your current panels, raising their heat resistance without buying all-new curtains.