Do blackout curtains keep a room cooler in summer?

Yes, on windows the sun actually reaches, and the effect is largest on east and west exposures. A closed panel intercepts direct sunlight before it lands on your floor and furniture, which stops the heat gain rather than removing it afterward. On a north-facing window in the northern half of the US there is almost no direct sun to block, so the benefit there is small. The single most important habit is closing the covering before the sun arrives at that window, not after the room has already warmed up.

Are blackout curtains better than thermal curtains for heat?

They are usually the same product with a different word on the package, and neither term is regulated. For summer heat, what matters is not opacity but the color and reflectivity of the face pointing at the sun, plus how closely the panel seals at the edges. A light or reflective outward face performs better in summer than a dark one, because a dark panel absorbs the sun's energy and then re-radiates part of it into the room. For winter, mass and layers matter more than color.

How much can curtains cut a cooling bill?

Less than the listings imply and more than nothing. Field studies summarized by the Department of Energy's Building America Solution Center found whole-home summertime cooling savings of 15% to 25% from the optimized use of high-efficiency shades, and 12% to 14% heating savings in winter. Two caveats matter: that range covers insulating cellular shades and exterior shading, which outperform fabric drapes, and 'optimized use' assumes the coverings are actually closed at the right times every day. A $40 pair of blackout panels lands at the modest end.

Do blackout curtains make a room hotter?

A dark panel in direct sun does get hot — sometimes uncomfortably hot to touch — because it absorbs the solar energy it stops. That heat then radiates partly into the room and partly back out through the glass. The net effect is still a cooler room than no covering at all, because much of the energy leaves through the window, but it is why a light-colored or reflective-backed panel is measurably better in summer than a black one. If the panel is scorching by mid-afternoon, that is a signal to reflect rather than absorb.

What works better than curtains for blocking heat?

Anything on the outside of the glass. Shade stops being an indoor problem the moment you intercept the sun before it enters — which is why the same DOE-summarized research found exterior shades cut dangerous indoor hours in a heat wave by about 55% against roughly 18% to 23% for interior shades. In practice that means awnings, exterior roller shades, solar screens, or a deciduous tree on the west side of the house. Indoors, insulating cellular shades outperform drapes. Curtains are the cheapest option, not the best one.

Do Blackout Curtains Help With Heat? The Honest Answer

Written & researched by Derek Holt Home & Appliances Editor

Updated October 2026

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Yes — but at the margin, not as a substitute for insulation or better windows. A closed blackout panel blocks direct sunlight before it lands on your floor, which prevents heat gain instead of removing it later, and heavy lined panels also slow heat moving through the glass. Field studies summarized by the Department of Energy put optimized shading at 15% to 25% whole-home cooling savings — but that range describes high-efficiency cellular and exterior shades, and a $40 pair of curtains sits at the low end of it. Real effect. Modest size.

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How does a curtain actually reduce heat?

Three separate mechanisms are at work, and they matter in very different amounts. Sorting them out explains why one curtain helps a lot on a west window and barely registers on a north one.

Blocking radiant solar gain is the big one and it only applies when the sun is physically striking the glass. Direct sunlight arriving through a window is a large, concentrated heat load — an unshaded window in summer sun can put more heat into a room than several people and appliances combined. A closed opaque panel intercepts it. That is the mechanism doing most of the work in July.

Slowing conductive and convective transfer is the mechanism the word "thermal" refers to. A heavy panel hung close to the glass traps a layer of still air, and still air is a reasonable insulator. This matters much more in winter, when the temperature difference across the glass is large and there is little sun, than in summer.

Reflecting energy back out depends entirely on the color of the surface facing the window. A pale or reflective outward face sends part of the solar energy straight back through the glass. A black face absorbs it, heats up, and then re-radiates some of that heat into your room. This is why the highest-performing summer panel is often not the darkest one.

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What do the measured numbers actually say?

The best-sourced figures available for US homes come from the Department of Energy's Building America Solution Center, which summarizes field research on window attachments. Two findings are worth quoting directly.

On energy: "DOE field studies have demonstrated whole home summertime cooling savings ranging from 15% to 25% from the optimized use of high-efficiency shades (both interior and exterior)," with "wintertime heating savings of about 12% to 14%."

On heat safety, which is the more striking result: modeling a 2021 heat wave in a home without air conditioning, the same source reports that "interior roller shades showed a reduction of about 18%, insulating interior shades showed a reduction of about 23%, and exterior shades showed a reduction of about 55%" in dangerous indoor hours.

Covering	Reduction in dangerous hours (2021 heat wave modeling)	Cost per window
Interior roller shade	~18%	$20–$60
Insulating interior shade (cellular)	~23%	$60–$250
Exterior shade	~55%	$150–$600

Read that table and the hierarchy is unmistakable: the further outside the glass you intercept the sun, the more it helps, and the gap between inside and outside is not incremental. It is roughly a factor of two and a half.

Why the listings overstate it

Three things get quietly dropped when those percentages appear in marketing copy.

"High-efficiency shades" is not a curtain. The 15% to 25% range includes insulating cellular shades and exterior products. A fabric drape, however heavy, lands at the bottom of that band.
"Optimized use" assumes discipline you probably will not have. The savings depend on the coverings being closed before the sun reaches the glass and opened afterward, every day, all season. Most households close them when the room is already hot, which captures a fraction of the available benefit.
A percentage of window heat transfer is not a percentage off your bill. Windows are one component of the building envelope. If your attic is under-insulated or your ducts leak, those dominate, and curtains will not show up in the numbers.

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How to get the most out of the curtains you already own

Close them before the sun arrives. East windows in the morning, west windows from early afternoon. Pre-emptive shading is worth several times as much as reactive shading.
Prioritize west, then east, then south. West is worst, because late-afternoon sun arrives at a low angle straight through the glass while the house is already at its warmest. North-facing windows in most of the US get little direct sun and are a low priority.
Point something light outward. If your panels are dark, a white-lined or reflective backing changes the summer math. Some owners simply add a cheap white liner behind an existing dark panel.
Seal the edges. A wraparound rod, a drop to the floor, and enough width to overlap. Hot air rolling over the top of a panel and down the glass defeats part of the point.
Open the house at night if the outside air is cooler. Curtains block gain; they do not remove heat that is already indoors. Night flushing does. Our guide to cooling a room without AC covers the sequence.

Which curtain, if heat is the reason you are buying?

Weight and edge sealing come first, then the color of the outward face. A dense triple-weave or dual-layer lined panel with a back-tab top on a wraparound rod is the configuration that performs; a thin grommet panel hanging two inches off the wall is mostly decorative.

Two that owners rate well for this specific job: the NICETOWN heavyweight thermal panels (paid link), which are the heaviest mainstream option at a normal price, and the BGment white thermal insulated panels (paid link), which put a pale reflective face toward the sun while keeping a dark blocking layer inside. The full field is in our thermal curtain picks and blackout curtain picks.

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What beats curtains, if you are willing to spend more

In order of effect per dollar on a hot window:

Exterior shading — an awning, an exterior roller shade, a solar screen, or a deciduous tree on the west side. This is the intervention with real leverage, because the sun never reaches the glass.
Insulating cellular shades inside the frame. Better than drapes in both the cooling and the heat-wave figures above, and they sit in the reveal so the perimeter gap is small.
Low-E window film on a sun-facing window, which cuts solar gain without blocking the view. Cheaper than glazing, permanent, and it works when nobody is home to close anything.
Air sealing and attic insulation. Not glamorous, usually the highest return per dollar in an older house, and completely independent of what you hang at the window.

Do they help in winter too?

Yes, through the trapped-air mechanism rather than the shading one, and the effect is smaller: the DOE-summarized figure is about 12% to 14% heating savings for optimized high-efficiency shades. What owners notice more than the bill is the draft. A cold pane chills the air touching it, that air sinks and slides across the floor, and it reads as a draft even when the window is perfectly sealed. A floor-length heavy panel intercepts it, which is why the drop length matters more in winter than the fabric does.

One winter caution: sealing a panel tightly against cold single glazing traps moisture at the sill, and standing moisture on a wooden sill is how mold gets started. Open the coverings during the day and wipe the sill when you see condensation.

The honest bottom line

Blackout curtains help with heat. They are the cheapest window intervention available, they work best on west and east exposures, and the benefit depends more on when you close them and how well they seal at the edges than on which pair you bought. What they are not is insulation, glazing or a cooling system. If your house is genuinely overheating, the money goes further on exterior shading, cellular shades or air sealing — and the curtains remain a sensible, inexpensive part of the answer rather than the whole of it.

Do Blackout Curtains Help With Heat?