Thermal vs Blackout Curtains: Are They the Same? | Ona

Updated October 2026 · By the Ona team

This guide explains what each label means and what it doesn't. It covers when one curtain does both jobs and what independent research says about curtains and heat. It also shows how to size and hang curtains so they block light and hold warmth.

In this guide

• Thermal vs blackout at a glance
• What each claim means, and what it doesn't
• Are blackout curtains thermal?
• Are thermal curtains blackout?
• What are thermal blackout curtains?
• How light and heat get past a curtain
• What research says about curtains and heat
• Which one do you need?
• How to hang curtains for light and warmth
• Ona's thermal and blackout curtains
• Questions, answered

Thermal vs blackout at a glance

	Blackout	Thermal (insulated)	Thermal blackout
What the word is about	Light passing through the fabric	Heat moving through the window	Both
How it works	An opaque layer stops light inside the cloth	Dense fabric or a lining holds still air between the curtain and the glass	An opaque, dense or lined build that aims to do both
Common builds	Coated back, triple weave with a dark core, or a sewn-in lining	Lined or interlined fabric, a foam-coated back, heavy weaves	Usually a coated back or a lining
What it doesn't promise	A dark room. Light still gets in at the top, sides, center and hem	A warm room or lower bills. Air still moves around the edges	Either of those
What decides the result	Fit: height, width, overlap, length	Fit: closed top, sealed sides, hem at the sill or floor	Fit, for both
Choose it when	Light is the problem: early sun, day sleep, a nursery, a screen	Temperature is the problem: a cold, drafty or sun-baked window	You have both problems in one room

Most labels are self-declared. Few retail curtain listings name a test method for either word, so read them as the maker's description, not a rating.

What each claim means, and what it doesn't

These are the words you'll see on curtain listings. The last column shows how Ona uses each one. Every Ona light and heat claim comes from a supplier listing. Ona has not tested any style, and none carries a rating.

Claim on the label	What it means	What it doesn't mean	How to check	On Ona's curtains
Blackout	The fabric is made to stop light passing through it	A dark room. Light still enters around the edges	Hold it up to a bright window. Ask whether the claim was tested or is supplier-listed	Grommet pair, wide panel, back-tab pair: supplier-listed 100% blackout fabric. Light can still enter at the top, sides and center
100% blackout	The maker says no light passes through the fabric itself	100% of the light is kept out of the room	Look for a test method or a measured figure. Most listings have neither	As above: supplier-listed, not tested by Ona
Room darkening	The fabric dims daylight noticeably	Blackout. Some light passes through the fabric	Check whether the curtain is lined; unlined fabric lets more light through	Velvet pair: room-darkening, unlined, not full blackout
Thermal / thermal insulated	Made to slow heat moving through the window	A set temperature change, warmer room or lower bill	Look for a rating such as an R-value. Most curtain listings have none	All four styles: listed by the supplier as thermal insulating; no insulation rating
Thermal blackout	Sold as both light-blocking and insulating	That both claims were tested	Check each claim separately	Grommet pair, wide panel, back-tab pair carry both supplier-listed claims
Lined	A second layer is sewn behind the face fabric	Blackout or thermal by itself	Check what the lining is for: light, heat or drape	Grommet pair, wide panel and back-tab pair are lined. Velvet is unlined
Energy saving	The maker says the curtain can reduce heating or cooling use	A saving in your home. That depends on the window, climate and fit	Look for the test conditions behind any percentage	Ona makes no energy-saving claim

Are blackout curtains thermal?

Not automatically. A dense, lined blackout curtain adds some insulation, because it holds a layer of still air against the window. But it is only made to insulate if it is also sold as thermal, and fit matters more than fabric.

Opacity and insulation are different properties. A coating that stops light also tends to stop air from passing through the cloth, and that helps. Cornell Cooperative Extension's fact sheet on window treatments puts it plainly: a window treatment "is effective only when it traps and holds air between itself and the window." The same fact sheet says installation matters more than fabric type, as long as little air can pass through the fabric.

So a blackout curtain hung on the trim, ending at the sill, with gaps at the sides, will block light through the fabric and do little for heat. The same curtain hung high, wide and to the floor does more of both.

Are thermal curtains blackout?

Not always. A curtain can be made to insulate and still let light through. Check for a separate blackout claim.

Many thermal curtains use a heavy face fabric or a lining that isn't fully opaque. That holds air without stopping light. Velvet is a common example. Ona's velvet pair is listed by the supplier as thermal insulating, but it is unlined and room-darkening, not blackout. It softens daylight and adds privacy, and some light comes through. The shade and your window's light affect how much.

If you want both darkness and warmth from one curtain, look for both claims on the same product.

What are thermal blackout curtains?

Thermal blackout curtains are sold for both jobs: an opaque layer stops light passing through the fabric, and a dense or lined build is meant to slow heat.

The three common builds:

• Coated back. A foam or acrylic coating on the side that faces the glass. It stops light and most air passing through the cloth, and it can feel stiffer.
• Triple weave. A dark yarn woven into the middle of the fabric. It blocks light inside the cloth and usually drapes more softly than a coated back.
• Lined. A separate blackout or thermal lining sewn behind the face fabric. Cornell's fact sheet recommends a separate lining for heat, because the layer of air between the two fabrics adds a little insulation.

Three Ona styles carry both claims: the grommet pair, the wide grommet panel and the back-tab pair. All three are lined, with a textured face and a blackout backing. Both claims are supplier-listed, and neither has been tested by Ona.

How light and heat get past a curtain

Light travels in straight lines. It gets past a curtain in two ways: through the fabric, which blackout fabric stops, and around the edges, which only fit can stop.

Heat has more routes. Cornell's fact sheet names four: radiation (your body heat radiating toward cold glass), convection (air moving), conduction (heat passing through the glass) and air leaking in around the window frame.

Convection is the one curtains handle worst. Cornell describes a "tunnel" between the curtain and the glass. Warm room air enters at the top, cools against the glass, sinks and pours out under the hem. Then it warms in the room and goes round again.

The same gaps leak both. The gap at the top that lets a line of light in also lets warm air into the tunnel. The gap at the sides lets in light and lets air move. The fixes for a darker room and a warmer room are therefore mostly the same: close the top, cover the sides, meet in the middle and reach the floor.

What research says about curtains and heat

These figures describe curtains in general, measured over single-glazed windows. They are not measurements of any Ona curtain. Ona's curtains have not been tested, so we can't place them on this scale.

Window treatment (general, single-glazed window)	Approx. reduction in window heat loss	Source
Drapery, conventionally hung on a traverse rod	5–10%	Cornell Cooperative Extension, 2000
"Most average draperies"	Up to 10%	U.S. Department of Energy, 2024
Drapery in tightly woven fabric with a separate lining, sealed at all four edges	25%	Cornell Cooperative Extension, 2000
Tightly installed cellular shades	About 40%	U.S. Department of Energy, 2024

Two things stand out. First, the same kind of curtain more than doubles its effect when it is lined and sealed at the edges. Second, curtains are a modest layer of insulation. They add comfort near a cold window; they don't replace good windows or weather-stripping.

Which one do you need?

Your main problem	What to look for	Ona styles to consider
Early sun wakes you, you sleep by day, or a nursery needs naps	Blackout fabric, then fit for the edges	Grommet pair, back-tab pair or wide panel (supplier-listed 100% blackout fabric)
A bedroom that is both bright and cold	Both claims on one curtain, hung high, wide and to the floor	Grommet pair, back-tab pair or wide panel
A cold or drafty living room where you want daylight	A thermal claim, a lining, and the habit of opening by day and closing at night	Any of the four. For the coldest windows, start with a lined style
A sun-facing window that overheats in summer	Close it during the hottest hours. A light or reflective side facing the glass reflects more sun than a dark one	Any style, closed during peak sun. Ona makes no heat-blocking claim
Deep color and softer light, without full blackout	Room-darkening fabric	Velvet pair (unlined, room-darkening)
A media room or screen glare	Blackout fabric, a closed top and a center overlap	Grommet pair, back-tab pair or wide panel

How to hang curtains for light and warmth

These steps work for blackout, thermal or both. The numbers use Ona's fit guidance and the placements in our guide to how high to hang curtains.

1. Seal the window first. Caulk and weather-strip any drafts around the frame. Cornell's fact sheet says this comes first and helps any interior window treatment work.
2. Mount the rod above the frame. Go at least 4–6″ above the window trim, or higher. A closed top matters most for heat: a cornice board, or a rod set close to the ceiling, closes the top of the tunnel. The more fabric above the window, the farther light must travel to escape over the top.
3. Extend the rod past both sides. Many guides suggest at least 4–6″ per side; 8–12″ lets the closed panels cover the trim and some wall as well. A wraparound (return) rod brings the outer edges back to the wall. Measure the rod width without the decorative finials.
4. Buy enough width to close fully. Start with 2× the rod width in total flat fabric. Ona sizes are flat widths per panel, and the folds take up some of that width. Cornell suggests about a 4″ overlap at the center for sealed draperies. A clip or magnet can hold the leading edges together.
5. Choose a length that reaches the floor. Measure from where the fabric top will sit down to the floor, then pick a hem. Ona's hem guide: float (½″ above the floor), floor kiss (0″) or puddle (+4″). A kiss or a puddle closes the bottom of the tunnel best. If a radiator or window seat sits below, end at the sill.
6. Keep heat sources clear. Don't trap a heating vent or radiator behind the curtain. Cornell suggests a deflector that sends the warm air into the room instead. Keep fabric well away from space heaters.
7. Use them by the season. In winter, open curtains on sunny south-facing windows during the day and close them at night, as the Department of Energy advises. Cornell adds that coverings on north-facing windows can stay closed around the clock. In summer, close curtains on sun-facing windows during the hottest hours.

Worked example: one 54″ window

The window trim is 54″ wide. Extend the rod 8″ past each side: 54 + 8 + 8 = 70″ rod. At 2× fullness you need 70 × 2 = 140″ of total flat fabric.

The formula: panels = (rod width × 2) ÷ flat width of one panel, rounded up to an even number so the curtains open from the center.

• Wide panels: 140 ÷ 70 = 2 → 2 wide panels
• 42″ panels: 140 ÷ 42 = 3.3 → 4 panels, or 2 pairs
• 52″ panels: 140 ÷ 52 = 2.7 → 4 panels, or 2 pairs

Option	Total flat fabric	Fullness on a 70″ rod	Verdict
1 pair, 52″ panels (2 panels)	104″	1.5×	Lighter folds; closes with little overlap
2 wide panels, 70″ each	140″	2.0×	Exactly 2×: full folds, room to overlap
2 pairs, 42″ panels (4 panels)	168″	2.4×	Fuller; closes with a generous overlap
2 pairs, 52″ panels (4 panels)	208″	3.0×	Very full; a deep stack when open

Order all the panels for one window together.

For length, measure the drop from the planned fabric top to the floor:

• An 84″ drop takes an 84″ panel for a floor kiss.
• A 96½″ drop takes a 96″ panel for a ½″ float.
• A 104″ drop takes a 108″ panel for a 4″ puddle.

The wide panel comes in 90″, 96″ and 108″ only, so it suits the last two.

The curtain calculator does this math with Ona's real sizes. The measuring guide shows where to put the tape.

Ona's thermal and blackout curtains

Every Ona style is listed by the supplier as thermal insulating, with no insulation rating. Three are also supplier-listed as 100% blackout fabric. The velvet is room-darkening.

	Linen Texture Blackout Grommet Pair	Back-Tab & Rod-Pocket Blackout Pair	Linen Texture Blackout Wide Grommet Panel	Velvet Room-Darkening Grommet Pair
Light	Supplier-listed 100% blackout fabric	Supplier-listed 100% blackout fabric	Supplier-listed 100% blackout fabric	Room-darkening, not full blackout
Thermal	Listed by the supplier as thermal insulating; no insulation rating	Same	Same	Same
Construction	Lined: textured face, blackout backing	Lined: textured face, blackout backing	Lined: textured face, blackout backing	Unlined velvet; supplier specifications list 100% polyester
In the set	1 pair · 2 panels	1 pair · 2 panels	1 panel	1 pair · 2 panels
Heading	Metal grommets	Hidden back tabs and a 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
Price	$189–$239 per pair	$189–$219 per pair	$139–$159 per panel	$139–$149 per pair

"Linen texture" and "linen-look" describe how the fabric looks, not its fiber. "Linen" is also a color name. Blackout here means supplier-listed 100% blackout fabric, not a promise of a dark room.

What we can and can't tell you. The blackout and thermal descriptions come from supplier listings. Ona hasn't tested any style for light or insulation. None has an R-value, a lab result or a measured light figure, so we don't quote a temperature change, energy savings or "total darkness". What we can stand behind is which styles are lined, the exact flat size of every panel, and how to hang them so they do as much as a curtain can. Room images on our site are styling visualizations, not proof of color, size or opacity. For care, follow the sewn-in care label.

Want to know how much difference a curtain can make in winter? Read do thermal curtains work?

Questions, answered

Are thermal and blackout curtains the same?

No. Blackout describes how much light passes through the fabric, and thermal describes how much the curtain slows heat moving through the window. One curtain can be sold as both, which is what "thermal blackout" means.

Are blackout curtains thermal?

Not automatically. A dense, lined blackout curtain adds some insulation by holding still air against the window, but only a thermal claim tells you it was made to insulate. How it's hung matters more than the fabric.

Are thermal curtains blackout?

Not always. A curtain can insulate and still let light through, so check for a separate blackout claim. Ona's velvet pair, for example, is listed by the supplier as thermal insulating but is room-darkening, not blackout.

What are thermal blackout curtains?

They are curtains sold for both jobs: an opaque layer stops light passing through the fabric, and a dense or lined build is meant to slow heat. Common builds are a coated back, a triple weave or a sewn-in lining.

Are thermal blackout curtains good?

They suit a room that is both bright and cold, such as a bedroom, because one curtain covers both problems. How well they work depends on fit: hang them above and past the frame, down to the floor, and close them fully.

Which is better, thermal or blackout curtains?

Neither is better in general. Choose blackout if light is the problem and thermal if a cold or hot window is the problem. If you have both, choose a curtain sold as both.

Do blackout curtains keep heat out in summer?

They can help on sun-facing windows when closed during the hottest hours, because they block direct sun. A light or reflective side facing the glass reflects more sun than a dark one. Ona makes no heat-blocking or temperature claim for its curtains.

Do thermal curtains keep the cold out?

They slow heat loss rather than stop it. Cornell Cooperative Extension reports that conventionally hung draperies cut window heat loss by 5–10%, and lined, tightly woven draperies sealed at all four edges by about 25%, over single-glazed windows.

Do blackout curtains have to be dark?

No. Blackout comes from the backing, coating or weave, not the face color. Ona's supplier-listed blackout styles come in light colors such as Ivory, Light Beige and Greyish White as well as darker ones.

Is velvet thermal or blackout?

Velvet is a fabric, not a rating, so it depends on the curtain. Ona's velvet pair is listed by the supplier as thermal insulating, is unlined, and is room-darkening rather than blackout.

Have Ona's curtains been tested for light or heat?

No. The blackout and thermal descriptions come from supplier listings. Ona hasn't tested any style, and none has an insulation rating or a measured light figure.

Sources

• Cornell Cooperative Extension, Department of Design and Environmental Analysis, Cornell University. Energy Saving Window Treatments, Housing Fact Sheet, reviewed and revised October 2000 (Mark Pierce). https://monroe.cce.cornell.edu/resources/energy-saving-window-treatment
• U.S. Department of Energy, Energy Saver bulletin. Let in the sunshine for energy savings!, March 1, 2024. https://content.govdelivery.com/accounts/USEERE/bulletins/38e1854
• Ona product facts: live product listings, October 2026. Blackout and thermal descriptions are supplier-listed and have not been independently tested.