Guide
Do blackout curtains keep heat out?
Partly, and a dark panel can work against you. The mechanism is absorption, and it is the one thing the label on the packet never mentions.
By Janet H. · Last updated October 17, 2026 · How we choose
Blackout curtains keep some heat out, and a dark one can make an afternoon room warmer rather than cooler. Blackout fabric absorbs solar energy and re-radiates part of it into the room; a light-colored or silver-backed panel reflects that energy at the glass instead, which is the construction you actually want for heat. Overnight in winter the same panels help, because they slow heat loss through the pane.
This is the most common mismatch in the whole category. "Blackout" describes what a fabric does to light. Thermal performance is a separate property, decided by color, coating and how closely the panel seals - and the two get sold together on the same label as though one implied the other.
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Mechanism
What happens when the sun hits a closed curtain
Sunlight passes through the glass and lands on the fabric. Whatever the fabric does not reflect, it absorbs, and absorbed energy becomes heat in the panel. A dark panel absorbs most of it, warms up, and then radiates that warmth into the room and convects it off both faces. The light is gone - the energy is not.
That is why people hang heavy dark blackout curtains in a west-facing bedroom, find the room is just as hot, and conclude curtains do nothing for heat. The curtains did something: they moved the heat from sunlight-on-your-skin to warm-fabric-in-your-room, which feels similar and sometimes worse.
Three variables
What changes the outcome
The color facing the glass
This is the big one, and it is free. A pale or silver surface facing the pane reflects a share of the radiation back out before the fabric can absorb it. Because only the glass-facing side matters thermally, you can have a dark room-side color and still get the reflection - which is exactly what a silver-backed thermal panel is.
Whether the panel seals at the edges
Heat moves around a curtain as readily as light does. A panel hung inside the recess leaves a convection path at top, sides and bottom, and warm air simply circulates past it. Mounting wider and higher than the frame with returns at each end is what closes that path - the same fix as for light gaps, described in how to fix curtain light gaps.
Which side of the glass you are working on
Everything inside the window acts after the energy is already through the pane, which caps how much any curtain can achieve. An exterior shade stops the radiation before it arrives, which is why it outperforms every interior option on summer heat. That ordering does not change with price or brand.
| Setup | Summer heat gain | Winter heat loss |
|---|---|---|
| Bare window | Worst | Worst |
| Dark blackout panel, inside mount | Little better; can feel warmer | Better - slows the cold draft off the pane |
| Light or silver-backed thermal panel | Noticeably better | Better |
| Cellular shade, tight recess fit | Better | Best of the interior options |
| Exterior shade or awning | Best by a wide margin | No benefit |
The winter side
What blackout curtains are genuinely good at thermally
At night, a cold pane cools the air beside it, that air falls and runs across the floor, and the room loses heat to the glass by radiation as well. A closed lined panel interrupts both: it blocks the radiant path and it traps a layer of still air between fabric and glass. This is real and it is why thermal curtains are sold as an energy product - the detail is in do thermal curtains save energy.
So the honest summary is seasonal. Blackout panels earn their keep on winter nights and on light control year round. For summer afternoons they need the right color and backing, or they are the wrong product.
Practical
A setup that handles both seasons
- 1Hang a light-colored or silver-backed thermal blackout panel, mounted wider and higher than the frame with returns.
- 2Close it before the sun reaches that wall, not after the room is already hot. Shading works on prevention.
- 3In winter, close it at dusk rather than at bedtime, so it is interrupting heat loss for the whole evening.
- 4If the room still overheats, add shading outside the glass. Nothing you hang indoors will match it.
Methodology
How we chose
We select on published construction and materials, on fitness for the specific problem each pick addresses, and on failure patterns that recur across owner feedback. We do not lab-test curtains and publish no heat-rejection or R-value figures of our own; where a figure appears it is the manufacturer's and is labeled as such. Full criteria on the methodology page.
What we’d buy
The products behind this advice
Picked against the criteria above, not the other way round. Prices are read from Amazon and refreshed daily; each link goes to the current listing.
| # | Best for | Product | Type | Construction | Price |
|---|---|---|---|---|---|
| 1 | Best for summer heat |  South and west-facing rooms that are uncomfortable by evening, where the panel needs to reflect rather than absorb. | Thermal curtain | Woven, silver coated | $38.49 · View on Amazon #ad Price as of November 3, 2026, and it can change. How we’re funded |
| 2 | Best all-round blackout |  Rooms where darkness is the main job and the heat is a secondary complaint you want help with overnight. | Blackout curtain | Triple-weave, uncoated | $19.99 · View on Amazon #ad Price as of November 3, 2026, and it can change. How we’re funded |
| 3 | Best if the room is still hot |  Anyone who has already hung heavy curtains and found the room no cooler — the fix is outside the glass. | Exterior shade | — | $159.00 · View on Amazon #ad Price as of November 3, 2026, and it can change. How we’re funded |
01 — Best for summer heat
Thermal Insulated Blackout Curtains, silver backed
Deconovo
A silver-tone thermal coating facing the glass reflects solar radiation back out before the fabric can absorb it — the mechanism that separates a genuinely heat-rejecting panel from a merely heavy one.
Who it’s for: South and west-facing rooms that are uncomfortable by evening, where the panel needs to reflect rather than absorb.
The catch: The coating is the failure point: it stiffens along fold lines and does not tolerate a hot wash or a tumble dryer. Expect a shorter life than an uncoated weave.
At a glance
- Type
- Thermal curtain
- Construction
- Woven, silver coated
- Care
- Gentle cold, no heat
- Drops
- 63 / 84 / 96 in
#ad Price as of November 3, 2026, and it can change. How we’re funded
02 — Best all-round blackout
Thermal Insulated Blackout Curtains
NICETOWN
Triple-weave polyester with no coating to crack or peel, machine washable, and sold in a wider ladder of drops than most ranges — including the 108-inch length a near-ceiling rod needs.
Who it’s for: Rooms where darkness is the main job and the heat is a secondary complaint you want help with overnight.
The catch: The grommet header holds the panel an inch off the wall with open gaps between grommets, so light still comes over the top. Add a pelmet, or choose a back-tab version, if that is your problem.
At a glance
- Type
- Blackout curtain
- Construction
- Triple-weave, uncoated
- Care
- Machine wash cold
- Drops
- 63 / 84 / 96 / 108 in
#ad Price as of November 3, 2026, and it can change. How we’re funded
03 — Best if the room is still hot
Outdoor Roller Shade with wand
Coolaroo
An exterior knitted shade the manufacturer rates at up to 90% UV block. Mounted outside the glass it stops solar radiation before it enters, which no interior covering can do.
Who it’s for: Anyone who has already hung heavy curtains and found the room no cooler — the fix is outside the glass.
The catch: Needs somewhere outdoors to mount — a soffit, beam or pergola — and has to be rolled up in high wind.
At a glance
- Type
- Exterior shade
- Fabric
- Knitted outdoor screen
- Operation
- Wand
- Fit
- Stock sizes
#ad Price as of November 3, 2026, and it can change. How we’re funded
FAQ
Questions people actually ask
Do blackout curtains keep heat out?
Some, and the color decides how much. A dark blackout panel absorbs solar energy and re-radiates part of it into the room, which is why a hot room often feels no better. A light-colored or silver-backed panel reflects more of it at the glass, and that is the construction to buy for heat.
Do blackout curtains make a room hotter?
A dark one in direct afternoon sun can, yes. The fabric absorbs the energy, warms up and radiates it inward, so the room gets the heat without the light. Reflective backing or a pale glass-facing color is what prevents it.
Do blackout curtains keep a room warmer in winter?
Yes, and this is where they do their best thermal work. A closed lined panel blocks the radiant path to a cold pane and traps still air behind the fabric, slowing both radiation and the convection current that runs down the glass and across the floor.
What color curtains keep a room coolest?
Light or reflective on the side facing the glass. What the room sees matters much less - a dark curtain with a pale or silver liner gives you the color you want indoors and the reflection you want at the window.
Are thermal curtains better than blackout curtains for heat?
Usually, because thermal panels are specified for the heat job: reflective backing, tighter weave, sometimes a bonded liner. Many products are both. If the label only says blackout, assume it was designed for light and check the backing before expecting a temperature change.
Keep going
Read next
Drafts
Best curtains to keep heat out
Reflect the sun before the fabric absorbs it — and why a dark blackout panel backfires.
Drafts
Best thermal curtains
Panels worth buying — and the sealing that doubles what any of them achieve.
Drafts
Do thermal curtains save energy?
Real effect, unquantifiable savings — and the four things that decide how much you get.
Drafts
Best window film to block heat
Film applied to the pane, what it realistically achieves against heat, and when shading beats it.
Blackout
Best blackout curtains for a room that's too bright
Panels that block light, plus the mounting rule that decides whether any of them works.
Drafts
Summer vs winter curtain setup
Same curtains, opposite routine — the free change most people never make.
About the author
Janet H.
Janet H. is the owner of Janet Media Group and the person behind Drape & Dawn. She researches every pick against the site's published methodology.
Published by Janet Media Group · Last updated October 17, 2026