Do Thermal Curtains Work? What to Expect | Ona
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Ona guides · Thermal & winter · Updated October 2026
Do Thermal Curtains Work? What to Expect
Yes, within limits. Thermal curtains slow heat loss through a window by holding a layer of still air between the fabric and the glass. How much they help depends mostly on fit: cover the frame, reach the floor, close the top, sides and center, and draw them at night. They don't stop drafts, and they don't replace sealing, storm windows or insulation.
Below: what independent research found, where curtains help and where they don't, how to hang them for a cold window, and a checklist for drafty windows. Already shopping? See thermal curtains.
Thermal curtains at a glance - They work by trapping air. A curtain insulates only while the air behind it stays still. - Fit beats fabric. Cornell Cooperative Extension says installation matters more than the type of fabric, as long as little air passes through the fabric. - Lined and floor-length do better. Heavy lined curtains beat coated thermal-backed ones in Consumer NZ's lab test, and its testers advise hanging curtains to the floor. - Seal first. A curtain can't stop cold air leaking around the frame. Caulk and weatherstripping can. - Use them on a schedule. Open sunny windows by day. Close every curtain at dusk. - Don't expect a rating. Curtains are rarely sold with an independent energy rating. Ona's have none.
What does "thermal" mean on a curtain?
Thermal curtains are made to slow heat moving through a window. You'll also see them sold as insulated curtains, thermal drapes or energy-saving curtains. Most pair a dense face fabric with a lining, an extra interlining, or a coated backing on the side that faces the glass.
The word describes intent, not a measured result. Curtains are rarely sold with an independent energy rating. The Attachments Energy Rating Council (AERC), the U.S. ratings program that the Department of Energy points shoppers to, lists shades, blinds, storm windows, solar screens and awnings among the products it covers. Curtains aren't on that list .
So judge a thermal curtain by two things you can check: how it's made (lined, tightly woven, long enough) and how you'll hang it.
How a window loses heat, and where a curtain helps
Heat leaves through a window in four ways. A curtain can help with three of them, and only when it's hung well.
| How heat escapes | What happens | Can a curtain help? | What fixes it best |
|---|---|---|---|
| Radiation | Your body heat radiates toward the cold glass, so you feel chilly near a window even in a warm room. | Yes. A closed curtain puts a layer between you and the glass. | Curtains, shades, low-e window film |
| Convection | Warm room air slips in at the top of the curtain, cools against the glass, sinks and pours out under the hem. Cornell calls this the "tunnel." | Yes, if the top, sides and bottom are closed. A short curtain with gaps keeps the loop going. | Closed edges, a floor-length hem, a closed top |
| Conduction | Glass is a good conductor and a poor insulator, so heat passes straight through it. | Somewhat. The still air behind a closed curtain adds a layer. | Storm windows, double glazing, insulating shades |
| Air leaks | Cold outdoor air leaks in around the sash, frame and trim. | No. The air is already inside by the time it reaches the curtain. | Caulk and weatherstripping |
Based on Cornell Cooperative Extension and the U.S. Department of Energy. See Sources.
What the research says
Good evidence on curtains is thin, and much of what you'll read comes from people who sell them, us included. These are the independent sources we found most useful.
Cornell Cooperative Extension (Energy Saving Window Treatments, revised 2000). Conventionally hung, unsealed draperies are "not efficient energy savers," mainly because of the tunnel of moving air behind them. Draperies do better when they're lined, closed at the top, sealed at both sides, overlapped at the center and long enough to touch the sill or floor. In Cornell's words, "the method of installation is more important in reducing heat loss than the type of fabric," as long as the fabric lets little air through. Cornell also recommends a separate lining for its extra layer of air. The fact sheet assumes single-pane windows, and it rates insulating shades and shutters ahead of draperies.
Consumer NZ (lab test of curtains and blinds, 2019). On a single-glazed test window in a room chilled to winter-night conditions, heavy lined curtains did better than coated thermal-backed ones. Its head of testing advises hanging curtains to the floor rather than stopping at the sill. Honeycomb (cellular) blinds were the best performers in the test.
University of Salford, Energy House (UK whole-house test facility). Researchers measured window coverings in a full-size test house, not a small lab box, to see how they behave with a real heating system (Fitton and colleagues, Energy Efficiency, 2017). The team still advises closing curtains and blinds on cold winter nights. It also reports that the saving across a typical year in its test house was small. What a curtain does at the window is not the same as what it saves across a whole home.
U.S. Department of Energy (Energy Saver guide, 2022). Close curtains and shades at night to protect against cold drafts. Open them during the day on south-facing windows to let in warming sunlight. For windows that still feel drafty after weatherizing, DOE suggests tight-fitting insulating shades, such as cellular shades.
Why there are no savings figures on this page
Published figures for curtains vary widely with the window, the curtain, the test and how the curtain is hung. A result measured at one window also doesn't carry over neatly to a whole home's heating. Rather than quote a number that may not fit your window, we describe what the research found and show how to get the most from the curtains you hang.
Are thermal curtains worth it?
Usually, if your windows feel cold and you're willing to hang the curtains properly. They're a reversible layer that also gives privacy, and darkness too if the fabric is blackout. They're the wrong tool for a window that leaks air, or for anyone who wants a measured energy saving.
| Your situation | Worth it? | Why |
|---|---|---|
| Single-pane or older windows; a chilly seat near the glass | Most likely | Single-pane glass loses much more heat than double-pane (Cornell), so a curtain has more to work with. It also blocks the chill radiating from the glass. |
| You can feel air moving at the window | Seal first | A curtain can't stop leaks around the frame. Caulk and weatherstrip, then add curtains. |
| Newer double-pane, low-e windows | A smaller difference | Less heat escapes in the first place. Buy curtains for comfort, privacy and light as much as for warmth. |
| You rent and can't change the windows | Often, yes | Curtains are reversible and move with you. Check your lease before you drill. |
| Large sliders or picture windows | Yes, if fully covered | More glass means more chill. Cover the full width and reach the floor. |
| You want a rated energy saving | Look elsewhere first | Cellular shades and storm windows are types AERC rates. Curtains aren't. |
How to hang thermal curtains so they actually work
The goal is a pocket of still air between the curtain and the glass, closed on all four sides. Each step closes part of the gap.
You'll need: a steel tape measure, painter's tape, a level, a step stool, and a rod with brackets. Optional extras are a cornice board, a wraparound (return) rod, and hook-and-loop tape or small magnets. Ona sells curtains only, not hardware.
- Seal the window first. On a windy day, look and feel for leaks around the sash, frame and trim. Weatherstrip the moving parts and caulk the fixed gaps. DOE and Cornell both put this first, because it helps every window covering work better.
- Mount the rod high and wide. Set it about 4–6″ above the frame and 6–12″ past each side, so the closed panels lap onto the wall around the window. Choose brackets that hold the rod close to the wall while still clearing the trim. More in how high to hang curtains.
- Buy enough width. Total flat fabric = 2 × rod width. Measure the rod end to end, leaving out the finials. Full panels can meet at the center and still reach the wall at the sides.
- Reach the floor. Measure from where the top of the fabric will sit down to the floor. Use that number to kiss the floor, add 4″ to puddle, or subtract ½″ to float. A kiss or a puddle closes the bottom of the tunnel best.
- Close the top. A cornice board, a shallow box over the rod, stops warm air from entering above the curtain. Without one, a rod mounted close to the ceiling leaves less room for air to slip in.
- Close the sides and center. A wraparound rod, or hook-and-loop tape on the outer edge and the wall, closes the sides. Cornell suggests a 4″ overlap at the center. On a single rod, a few small magnets or clips along the meeting edges keep the center closed.
- Use them on a schedule. Open the curtains on sunny, south-facing windows during the day, and close every curtain at dusk. Cornell adds that coverings on north-facing windows can stay closed around the clock if you can spare the daylight.
Keep heat sources clear. Don't let curtains cover, touch or hang over a radiator, baseboard heater, heating vent or space heater. The U.S. Fire Administration advises keeping anything that can burn at least 3 feet from heat sources, including radiators and space heaters. Where a heater sits under the window, check its manual for clearances before you choose any window covering.
What size thermal curtains do you need?
Two measurements decide it: the rod width, and the drop from the fabric top to the floor.
- Width. Rod width × 2 = total flat fabric. Divide that by one panel's width, then round up to an even number of panels if the curtains open in the center.
- Length. Measure from the fabric top to the floor. Floor kiss = 0″, puddle = +4″, float = −½″.
- Panels. Ona sizes are flat dimensions per panel. A pair is 2 panels, and the wide panel is 1. A 42″ pair gives 84″ of flat fabric, a 52″ pair gives 104″, and each wide panel gives 70″. Folds use some of that width.
| Rod width (without finials) | Flat fabric at 2× | Ona option | Fullness you get |
|---|---|---|---|
| 42″ | 84″ | One 42″ grommet pair (84″) | 2.0× |
| 52″ | 104″ | One 52″ pair (104″) | 2.0× |
| 60″ | 120″ | Two wide panels (140″), or one 52″ pair (104″) | 2.3× / 1.7× |
| 72″ | 144″ | Two wide panels (140″) | 1.9× |
| 84″ | 168″ | Two 42″ grommet pairs (168″) | 2.0× |
| 96″ | 192″ | Two 52″ pairs (208″) | 2.2× |
| 108″ | 216″ | Two 52″ pairs (208″), or four wide panels (280″) | 1.9× / 2.6× |
| 120″ | 240″ | Four wide panels (280″) | 2.3× |
For a cold window, lean toward the fuller option, so the panels still meet when they're stretched to the wall. When a window needs two pairs or several wide panels, order them together in one color .
Worked example. Take a 36″-wide bedroom window. Run the rod 8″ past each side: 36 + 8 + 8 = 52″ of rod. At 2×, that's 104″ of flat fabric, which is one 52″ pair. Say you plan the fabric top 86″ above the floor. There's no 86″ length, so choose 90″ for a 4″ puddle, which closes the floor gap well. An 84″ panel would float 2″ above the floor and leave the bottom of the tunnel open.
The curtain calculator does this math for any window, and the measuring guide shows how to take each measurement.
Cold, drafty-window checklist
Work from the top down. The early steps usually matter most, and they help everything after them work better.
1. Find the cold
- [ ] On a windy day, hold a lit incense stick or a smoke pen near the sash, frame and trim. If the smoke drifts sideways, you've found a leak (DOE). Keep the flame well away from curtains and other fabric.
- [ ] Check that each window shuts fully and that its sash lock is closed.
- [ ] Look for cracked caulk, worn weatherstripping and gaps around the trim.
2. Seal it
- [ ] Weatherstrip the moving parts of the window (DOE).
- [ ] Caulk the fixed gaps. Use foam sealant on larger gaps around the window trim (DOE).
- [ ] Renting? Ask before you caulk. Removable options exist, such as removable caulk and interior window film kits.
3. Add a layer at the glass
- [ ] For the coldest windows, consider interior or exterior storm windows, or low-e window film (DOE). NFRC rates window films, and AERC rates storm windows.
- [ ] On windows that still feel drafty, add a tight-fitting insulating shade, such as a cellular shade, inside the frame (DOE).
4. Hang the curtains for warmth
- [ ] Lined, tightly woven fabric (Cornell; Consumer NZ).
- [ ] Rod 4–6″ above the frame and 6–12″ past each side.
- [ ] Flat fabric of 2× the rod width.
- [ ] A hem that kisses the floor or puddles 4″.
- [ ] A closed top: a cornice board, or a rod close to the ceiling.
- [ ] Closed sides and center: a wraparound rod or hook-and-loop tape at the sides, and an overlap, magnets or clips at the center.
5. Use them well
- [ ] Open sunny, south-facing windows by day, and close every curtain at dusk (DOE).
- [ ] Keep radiators, baseboard heaters and warm-air registers clear of drapes (DOE). Keep anything that can burn at least 3 feet from heat sources (U.S. Fire Administration).
- [ ] Watch for condensation. A closed curtain keeps room heat off the glass, so the glass runs colder. If you find water on it in the morning, open the curtains, wipe the glass and sill, and air the room
. - [ ] Still cold? A home energy audit can find leaks and missing insulation elsewhere in the house (DOE).
Thermal curtains vs other window coverings
| Option | How it helps in winter | What it needs | Independent rating? |
|---|---|---|---|
| Unlined curtain, hung short or with gaps | Little. Cornell calls unsealed draperies "not efficient energy savers." | Nothing special, which is the problem | No |
| Lined, floor-length curtain, closed at the edges | More. Lining, length and closed edges all come out ahead in Cornell's and Consumer NZ's findings. | A wide rod, a floor-length hem, a closed top and sides | Not an AERC-rated type |
| Curtain with a coated "thermal" backing | Did not beat heavy lined curtains in Consumer NZ's test. | The same fit as any curtain | Not an AERC-rated type |
| Cellular (honeycomb) shade | The best performer in Consumer NZ's test. DOE suggests it for drafty windows. | A tight, inside-mount fit | AERC rates this type |
| Interior or exterior storm window | Adds a layer of glazing (DOE). | Weatherstripping at all moving joints | AERC rates this type |
| Low-e window film | Keeps heat from radiating out through the glass (DOE). | Careful application | NFRC rates films |
| Insulating shutters or panels | Cornell rates them ahead of both draperies and shades. | They block the view and daylight while closed | Varies |
| Caulk and weatherstripping | Stops air leaks, which no covering can. | Do it before adding any covering | Not applicable |
For a very cold window, the strongest setup is often a layer at the glass, such as a cellular shade or a storm window, with a lined, floor-length curtain over it. Layering helps: Consumer NZ found that hanging a blanket behind curtains "lifted heat retention dramatically," though few people want to do that every night.
Thermal vs blackout curtains
Thermal describes heat. Blackout describes light. A curtain can be both, either or neither, and a blackout curtain isn't automatically good at keeping out the cold. For winter, ask the same three questions of either kind: is it lined, does it reach the floor, and can you close the edges? Full comparison: thermal vs blackout curtains.
What about R-value?
R-value measures resistance to heat flow: the higher the number, the better a material insulates (DOE). It's the standard number for insulation. Curtains, though, are rarely sold with one, and no common rating program covers them.
A fabric's R-value also misses most of what happens at a real window. Air moving around the edges of a curtain can matter more than the fabric itself, which is why Cornell puts installation ahead of fabric type. If a listing quotes an R-value for a curtain, ask what was tested (the fabric alone, or the curtain hung on a window), how, and by whom.
Ona's curtains are listed by the supplier as thermal insulating; no insulation rating. We don't publish an R-value for them.
Do thermal curtains help in summer?
They can help on windows that get direct sun. DOE advises closing draperies on windows that receive direct sunlight on summer days, and suggests medium-colored draperies with white plastic backings to reduce heat gain. Ona makes no heat-blocking or temperature claim for any style.
Ona's thermal curtains, honestly
All four Ona styles are listed by the supplier as thermal insulating; no insulation rating. Ona hasn't tested them for insulation, so we don't promise a warmer room, a temperature change or a lower bill. What we can stand behind is how each style is made and sized, so you can hang it the way the research favors.
| Linen Texture Blackout Grommet Pair | Back-Tab & Rod-Pocket Blackout Pair | Linen Texture Blackout Wide Grommet Panel | Velvet Room-Darkening Grommet Pair | |
|---|---|---|---|---|
| Construction | Lined | Lined | Lined | Unlined |
| Thermal | Listed by the supplier as thermal insulating; no insulation rating | Same | Same | Same |
| Light | Supplier-listed blackout fabric | Supplier-listed blackout fabric | Supplier-listed blackout fabric | Room-darkening, not blackout |
| What you get | Pair · 2 panels | Pair · 2 panels | 1 panel | Pair · 2 panels |
| Heading | Metal grommets | Hidden back tabs and rod pocket | Metal grommets | Metal grommets |
| Flat width per panel | 42″ or 52″ | 52″ | 70″ | 52″ |
| Lengths | 63, 72, 84, 90, 96″ (42″ wide); 63–108″ (52″ wide) | 63, 72, 84, 90, 96, 108, 120″ | 90, 96, 108″ | 63–108″; not every color in every length |
| Colors | Light Beige, Linen, Greyish White, Sage Green, Light Grey, Dark Grey, Denim Blue, Black | Ivory, Linen, Light Beige, Sage Green, Cappuccino, Light Grey | Same 8 as the grommet pair | Dark Green, Burgundy, Dark Gray, Sage Green |
Blackout here means the supplier lists the fabric as blackout. Ona hasn't tested it, and light can still enter at the top, at the sides and where the panels meet. "Linen texture" describes the look of the fabric, not the fiber, and Linen is also a color name.
Which one for a cold window? Cornell recommends a separate lining, so start with a lined style. Choose the grommet pair for most windows, the back-tab pair for a tailored look or a window that needs 120″, and the wide panel for sliders and wide glass. Choose the velvet pair for its deep color and soft texture where full blackout isn't needed. It's unlined, so hang it with the same care.
Shop thermal curtains → · Find your size with the calculator
Free standard shipping to the US. Returns are accepted for damaged, defective or incorrect items only (refund policy).
Curious where thermal curtains are searched most? See where Americans search for thermal curtains.
Thermal curtain questions, answered
Do thermal curtains really work?
Yes, within limits. They slow heat loss by trapping still air between the fabric and the glass, and they work best when they're lined, reach the floor and are closed at the top, sides and center. Hung short or with gaps, they do little, according to Cornell Cooperative Extension.
Do thermal curtains keep the cold out?
They can make a cold window feel less chilly, but they don't stop drafts. Cold air leaking around the frame needs caulk and weatherstripping. Once that's done, the curtain adds a layer between the room and the cold glass.
Are thermal curtains worth it?
Usually, for single-pane or older windows and for seats near cold glass, as long as you hang them properly. For drafty windows, seal the leaks first. If you want an independently rated energy saving, look at AERC-rated cellular shades or storm windows.
How do I keep cold air from coming through my windows?
Find and seal the leaks first: weatherstrip the moving parts and caulk the fixed gaps. Then add a layer at the glass, such as a storm window, low-e film or a cellular shade, and finish with lined, floor-length curtains that you close at night.
What kind of curtains keep the cold out best?
Lined, tightly woven, floor-length curtains, hung wide and closed at the edges. In Consumer NZ's lab test, heavy lined curtains did better than coated thermal-backed ones, and its testers advise hanging curtains to the floor rather than to the sill.
Do blackout curtains keep the cold out?
Only as well as they're made and hung. Blackout describes light, not heat. A lined blackout curtain that reaches the floor and closes at the edges can help in winter, while a short one with gaps won't do much.
Are thermal curtains the same as blackout curtains?
No. Thermal describes heat and blackout describes light. One curtain can be listed as both: three Ona styles are supplier-listed as blackout fabric and as thermal insulating.
Do thermal curtains work in summer?
They can help on windows that get direct sun if you close them during the hottest hours. DOE recommends closing draperies on sunny windows on summer days. Ona makes no heat-blocking or temperature claim.
What is the R-value of thermal or blackout curtains?
Most curtains have no published R-value, and no common rating program covers them. Ona's curtains are listed by the supplier as thermal insulating, with no insulation rating, so we don't quote an R-value.
Will thermal curtains lower my heating bill?
Not by an amount anyone can promise. Results depend on your windows, climate, heating and how the curtains are hung, and a whole-house test at the University of Salford found the yearly saving from closing curtains was small. Ona makes no energy or bill-savings claim.
Should thermal curtains touch the floor?
Yes, where nothing is in the way. A hem that kisses the floor (0″) or puddles (+4″) closes the bottom of the air gap behind the curtain. Keep fabric clear of radiators, heaters and vents.
Should I keep thermal curtains closed during the day in winter?
Open them on sunny, south-facing windows during the day to let the sun in, and close them at dusk. According to Cornell, coverings on north-facing windows can stay closed if you don't need the daylight.
Can I hang thermal curtains over a radiator or heater?
No. Don't let curtains cover or touch a radiator, baseboard heater, vent or space heater. The U.S. Fire Administration advises keeping anything that can burn at least 3 feet from heat sources, so check the heater's manual for clearances before you choose any window covering.
Do thermal curtains cause condensation?
They can make it more noticeable. A closed curtain keeps room heat off the glass, so the glass runs colder and moisture can condense on it. Open the curtains in the morning, wipe the glass and air the room.
Which side of a thermal curtain faces the window?
The lining or backing faces the glass, and the decorative face faces the room. On Ona's lined styles, the lined back goes toward the window.
Are Ona's curtains thermal?
All four Ona styles are listed by the supplier as thermal insulating, with no insulation rating. Three are lined; the velvet pair is unlined and room-darkening. Ona hasn't tested any of them for insulation.
How can I keep my house warm in winter?
Seal air leaks and add insulation first, and keep your heating system maintained. Then use your windows well: let the sun in by day, and close curtains and shades at night. DOE's Energy Saver guide covers each step.
How we made this guide
- We read the top Google results for "do thermal curtains work" on October 16, 2026, then went to the primary sources below. We used only sources we could open and read.
- Ona has not tested any curtain for insulation. Thermal and blackout descriptions of Ona products come from supplier listings.
- No one paid to be mentioned here. Reviewed October 2026.