What Are Blackout Curtains? How They Work | Ona
Share
Updated October 2026 · By the Ona team
Blackout curtains are curtains made with a fabric or lining that stops light from passing through the cloth. Most have an opaque layer behind the face fabric. That layer can be a coated backing, a woven black core or a sewn-in lining. The fabric stops the light, but the fit decides how dark the room gets, because light still comes in at the top, sides, center and hem.
This guide covers what blackout fabric and lining are, why light gets around even good blackout curtains, and how to size them for a darker room. It also compares them with blinds. Every number here works with a tape measure.
In this guide
- What blackout curtains are
- What they're made of, and how they work
- Why light still gets in
- How to size blackout curtains for a darker room
- Are blackout curtains worth it?
- Blackout curtains vs blinds and shades
- How to make curtains blackout
- Blackout vs thermal curtains
- How to choose blackout curtains
- Ona's blackout curtains
- Questions, answered
What blackout curtains are
The word "blackout" describes the fabric, not the room. It means the cloth is made to stop light from passing through it. It doesn't promise a dark room, because a curtain hangs in front of the window, not inside it.
Curtains sit on a scale by how much light passes through the fabric. The names aren't standardized, so check how each brand uses them.
| Type | Light through the fabric | After dark, with lamps on | Often chosen for |
|---|---|---|---|
| Sheer | Most daylight passes, and shapes show through | Little privacy | Layering, soft daylight |
| Light filtering | Soft, diffused daylight; the room stays bright | Some privacy; a lit room glows through | Living and dining rooms |
| Room darkening (also called "semi-blackout" or "dim-out") | Much less light, with some glow through the cloth | Good privacy | Bedrooms, TV rooms |
| Blackout | The fabric is made to stop light from passing through | High privacy | Bedrooms, nurseries, day sleepers, media rooms |
Most regular curtains, the unlined kind without a blackout layer, fall in the first two rows.
At Ona, three lined styles use 100% blackout fabric. The velvet pair is room-darkening and unlined, so it is not a blackout curtain. The full comparison is in blackout vs room-darkening curtains.
What blackout curtains are made of, and how they work
Light gets through an ordinary curtain in two ways: through the tiny gaps between the yarns, and through the yarns themselves. A blackout curtain adds a layer that closes both paths. Usually a dark core absorbs the light, and lighter outer layers keep both sides looking clean.
The face is the side you see in the room. It can be almost any fabric: a textured weave, velvet, cotton or polyester. On its own, a face fabric is rarely blackout. The layer behind it does that job.
The four common constructions
| Construction | How it stops light | How it feels and hangs | Watch for |
|---|---|---|---|
| Coated backing (foam-backed, "3-pass") | Layers of acrylic foam are applied to the back of the fabric. In a 3-pass coating, a black layer sits between two white ones. | Firmer, with a smooth or slightly rubbery back and crisper folds | Over time, heat and rough washing can crack or peel the coating |
| Triple weave | A black yarn is woven between two face layers, with no coating | Soft and fluid, close to a regular curtain | Often less opaque than a coated back, especially in pale colors |
| Sewn-in blackout lining (a lined curtain) | A separate blackout fabric is stitched to the back of the face fabric | Fuller, rounder folds, with more body and weight | Heavier on the rod, and two layers to care for |
| Separate liner | A blackout panel hangs behind any curtain, on the same rod or a second one | Adds bulk, and you can take it down | Its edges leak like any panel's, so size it to match the curtain |
What is blackout curtain lining? It is the opaque layer on the back of a blackout curtain. It may be a second fabric sewn on, a coating applied to the back, or a separate liner. The lining blocks the light. The face gives the color and texture.
Do blackout curtains have a plastic backing? Coated ones can feel that way. For a softer back, look for a triple weave or a fabric lining.
Where Ona's blackout styles fit
Ona's three blackout styles are lined curtains, each with a textured face and a blackout backing. The fabric is listed as 100% blackout. Ona has not independently tested light blocking.
"Linen texture" and "linen-look" describe how the face is woven, not what it is made of. "Linen" is also a color name.
Do blackout curtains have to be black?
No. The opaque layer blocks the light, so ivory, beige, sage and grey curtains can all be blackout. From the street, you see the back of the curtain. That is the lining or coating, or on a triple weave, the face color.
Why light still gets in: the four gaps
Blackout fabric stops light from passing through the cloth. It can't stop light from going around it. Curtain brackets hold the rod a few inches out from the wall, so the curtain hangs with a slot of air behind it. Light comes through that slot and bounces off the wall and ceiling. It shows up as a bright line around the window.
So when blackout curtains let light in, the cause is usually the fit, not the fabric.
| Where light gets in | Why | What helps |
|---|---|---|
| Top | Light rises over the heading, between the rod and the wall. A rod just above the frame leaves little fabric above the glass. | Raise the rod. Ona's guide starts 4–6″ above the frame, about 10″ for a taller line, or near the ceiling. A valance, cornice or pelmet board caps the top. |
| Sides | The panel edges stand away from the wall, and light spills around them. | Extend the rod past the trim on both sides, so the fabric covers wall as well as glass. A wraparound (return) rod turns each edge back to the wall. |
| Center | The two panels meet, but the folds pull them apart. | Buy enough fabric (2× the rod width) for the edges to meet without strain. A small magnet or clip at mid-height keeps them closed. A single panel drawn to one side has no center seam. |
| Bottom | The hem stops at the sill or floats above the floor. | Hang to the floor. Choose a floor-kiss (0″) or puddle (+4″) hem instead of a float (−½″). |
The heading matters at the top, too. Grommets sit below the fabric top and slide along the rod. Back tabs hold the rod behind the panel, and a rod pocket encloses it, so the rod is hidden.
The step-by-step fixes are in how to block light around curtains. To work on the whole room, including doors and other light sources, see how to darken a room, step by step.
How to size blackout curtains for a darker room
Size the curtains to the rod. Then size the rod to the wall around the window, not to the glass. Here is the method, using Ona's default fullness.
The formulas
- Rod width = trim width + overhang on the left + overhang on the right. Measure the rod without its finials.
- Total flat fabric = rod width × 2. That is Ona's default. Use 1.5× for flatter folds, or up to 3× for very full ones.
- Panels needed = total flat fabric ÷ flat panel width, rounded up. Use an even number to split them across both sides.
- Length = the distance from where the fabric top will sit down to the floor, adjusted for the hem.
Step by step
- Measure the window trim. Measure the width from the outside edge of the trim on one side to the outside edge on the other. Then measure the height from the floor to the top of the trim.
- Add overhang to set the rod width. Start with 6″ on each side, or 8–12″ for a darker room if the wall allows. The extra width also lets the open panels stack beside the glass, so you keep your daylight.
- Set the rod height. About 4–6″ above the trim gives a classic line, and about 10″ gives a taller one. A higher rod closes more of the top gap.
- Work out the fabric. Multiply the rod width by 2, then divide by the flat width of one panel.
- Set the length. Measure from where the top of the fabric will sit down to the floor. That is the floor-kiss length.
- Check the closed curtains. Once they're hung, the edges should meet in the middle with fabric to spare, and the hem should reach the floor.
Worked example. A bedroom window has trim 36″ wide, and the top of the trim is 80″ above the floor.
- Rod: 36″ + 8″ + 8″ = 52″
- Height: the rod goes about 10″ above the trim, so the fabric top sits about 90″ above the floor
- Fabric: 52″ × 2 = 104″ of flat fabric, or one pair of 52″ panels (2 × 52″)
- Length: 90″ for a floor kiss
- At Ona: the grommet pair or the back-tab pair, at 52″ × 90″ per panel
Rod width to panels, at about 2× fullness
| Rod width (no finials) | Flat fabric needed at 2× | One Ona option | Fullness you get |
|---|---|---|---|
| 42″ | 84″ | 1 grommet pair, 42″ panels (84″) | 2.0× |
| 52″ | 104″ | 1 pair, 52″ panels (104″) | 2.0× |
| 60″ | 120″ | 2 wide panels, 70″ each (140″) | 2.3× |
| 70″ | 140″ | 2 wide panels (140″) | 2.0× |
| 84″ | 168″ | 2 pairs, 52″ panels (208″) | 2.5× |
| 104″ | 208″ | 2 pairs, 52″ panels (208″) | 2.0× |
| 140″ | 280″ | 4 wide panels (280″) | 2.0× |
Every Ona width is the flat width of one panel, and the folds use some of it. A pair of 52″ panels has 104″ of fabric, but it suits a rod of about 52″, not 104″. Using more than one pair on a window?
The curtain calculator runs these numbers from your rod width and drop. The measuring guide shows each line on a drawing.
Are blackout curtains worth it?
Yes, if you want a darker room at set times and can hang the curtains wider and higher than the window. If a room needs daylight most of the day, light-filtering curtains usually suit it better. So does a blackout pair that you open each morning.
They tend to earn their place when:
- A bedroom faces a streetlight, a neighbor's porch light or early sun.
- Someone sleeps during the day, such as a shift worker.
- A nursery or kids' room is used for daytime naps.
- A TV room, media room or home office gets glare on the screen.
- You want more privacy after dark than a thinner curtain gives.
They're less useful when:
- The room is used mostly in daylight and the curtains will stay open.
- The rod can't extend past the frame, so the side gaps will stay.
- You want a light, airy look. Lined blackout panels have more body.
Should living room curtains be blackout? Only if the room doubles as a TV room or gets strong afternoon sun. Many living rooms suit light filtering better, or a blackout pair left open by day.
Budget for the rod, too. It needs to be long enough for the overhang and sturdy enough for lined panels, with a center support on long spans. Follow the rod maker's load limits.
Blackout curtains vs blinds and shades
Neither wins everywhere. A blackout roller shade mounted inside the frame leaves narrow gaps at its edges. Curtains leave wider gaps, but they cover the frame and the wall around it. For the darkest room, use both, with a shade inside the frame and curtains outside it.
| Blackout curtains | Blackout roller shade or blind | |
|---|---|---|
| Where it hangs | Outside the frame, on a rod above and beside the window | Inside the frame, or just outside it |
| Where light leaks | Top, sides, center seam and hem | Narrow strips at both edges, and around the roller at the top |
| How to shrink the gaps | Raise and widen the rod, add a return rod, close the center, hang to the floor | Measure the inside mount accurately. Some systems add side channels. |
| What it covers | The glass, the frame and some wall | Mostly the glass |
| Open, by day | The panels stack beside the glass if the rod extends far enough | Rolls up out of the way, though the roller housing still shows |
| Look | Soft folds that frame the window and add texture | Flat and minimal |
| Cords | None on a plain rod | Many have pull cords, though cordless versions exist |
| Works well for | Bedrooms, wide windows, sliding doors, and rooms that want softness | Deep window frames, and layering behind curtains |
Cords and children. The U.S. Consumer Product Safety Commission advises cordless window coverings in homes with young children (CPSC, October 2022). Curtains on a plain rod have no pull cords. If you choose a blind or shade, choose a cordless one.
Ona sells curtains only. A deeper comparison is in curtains vs blinds.
How to make curtains blackout
Add an opaque layer behind them, then close the gaps around them. Curtains that "don't work" usually need the second step more than the first.
| Option | How it works | Good for | Watch for |
|---|---|---|---|
| Fix the gaps first | Raise and widen the rod, close the center and lengthen the hem | Curtains that are already opaque but leak at the edges | Check the rod's reach before you buy new curtains |
| Hang a blackout liner | A separate blackout panel hangs behind the curtain, on the same rod with hooks or rings, or on the back rod of a double rod | Keeping curtains you love | The liner's edges leak too, so match its size to the curtain |
| Sew in blackout lining | Stitch blackout lining fabric to the back of each panel | Unlined curtains you plan to keep | It adds weight, and the care label may change |
| Add a blackout shade | Mount a roller shade inside the frame, with the curtains outside it | The darkest result | Two products to measure and fit |
| Cover the glass | Apply blackout film or removable panels directly to the glass | Rentals and short-term fixes | It blocks the view and daylight until you remove it |
| Replace them | Switch to lined blackout curtains sized to the rod | Thin or unlined curtains, or rods that need new panels anyway | Size by the rod, not the window |
Ona doesn't sell separate liners or hardware. Its three blackout styles are already lined, so there's nothing to add behind them.
Blackout vs thermal curtains
Blackout is about light, and thermal is about heat. The two overlap because the dense layer that stops light also adds a layer between the room and the glass. That's why many curtains are sold as both.
All four Ona styles are listed as thermal insulating. There is no insulation rating, so Ona doesn't quote temperature or energy savings. Fit matters here too: gaps at the top and sides let air move, just as they let light in. More in thermal vs blackout curtains.
How to choose blackout curtains: six checks
- How is the blackout made? Check whether it is coated, a triple weave or lined. Check, too, whether the claim has been tested or only listed on the spec.
- Is the size per panel or per pair? Ona lists every size as the flat size of one panel.
- Does the width suit your rod? Aim for about 2× the rod width in flat fabric.
- Does the length reach the floor from where the fabric top will sit?
- Which heading suits how you use them? Grommets slide easily if you open and close the curtains every day. Back tabs and rod pockets give a tailored top and hide the rod. Compare them in grommet vs rod pocket vs back tab curtains.
- What does the care label say? Coated backs often need gentler washing than plain fabric.
The full buyer's checklist is in how to choose blackout curtains. For lined and unlined curtains side by side, see lined vs unlined curtains.
Ona's blackout curtains
Ona has three blackout styles. All three are lined, and each is sold in flat sizes per panel.
| Grommet pair | Back-tab & rod-pocket pair | Wide grommet panel | |
|---|---|---|---|
| In the set | 1 pair · 2 panels | 1 pair · 2 panels | 1 panel |
| Width per panel (flat) | 42″ or 52″ | 52″ | 70″ |
| Lengths | 63–96″ (42″ panels); 63–108″ (52″ panels) | 63–120″ | 90″, 96″, 108″ |
| Heading | Metal grommets | Hidden back tabs and a rod pocket | Metal grommets |
| Construction | Lined: textured face + blackout backing | Lined: textured face + blackout backing | Lined: textured face + blackout backing |
| Light control | 100% blackout fabric | 100% blackout fabric | 100% blackout fabric |
| Thermal | Listed as thermal insulating; no insulation rating | Same | Same |
| Colors | 8 solid colors | 6 solid colors | 8 solid colors |
| Price | $189–$239 per pair | $189–$219 per pair | $139–$159 per panel |
- Light gaps still apply. Light can still enter at the top, sides and center. Hang the curtains high, wide and to the floor.
- Velvet is not blackout. Ona's velvet pair is room-darkening and unlined.
- What's included. Ona sells no rods, hooks or rings, and no custom sizes.
- Care. Follow the sewn-in care label. The back-tab pair is listed as machine washable.
- Shipping. Ona ships to the US only, and free standard shipping is shown at checkout.
- Images. Ona's room images are styling visualizations, not light tests.
Shop blackout curtains · Find your size
Blackout curtains: questions, answered
What are blackout curtains?
Blackout curtains are curtains made with a fabric or lining that stops light from passing through the cloth. The blackout comes from an opaque layer behind the face fabric, such as a coating, a woven black core or a sewn-in lining. How dark the room gets also depends on how the curtains are hung.
How do blackout curtains work?
An opaque layer behind the face fabric absorbs or blocks the light that would pass through the cloth. Light can still go around the curtain: over the rod, past the sides, through the center and under the hem. A wide, high, floor-length fit closes those paths.
Do blackout curtains block 100% of light?
Not on their own. Even when no light passes through the fabric, light can still enter at the top, sides and center where the panels meet. Ona's three blackout styles use 100% blackout fabric, and Ona has not independently tested light blocking.
Are blackout curtains worth it?
Yes, if you want a darker room at set times and can hang the curtains wider and higher than the window. Common examples are a bedroom near a streetlight, a room for daytime sleep and a TV room. For rooms used mostly in daylight, light-filtering curtains often suit better.
What is blackout curtain lining?
It is the opaque layer on the back of a blackout curtain. It can be a separate fabric sewn behind the face, a foam coating on the back, or a detachable liner hung behind the curtain. The lining blocks the light, and the face gives the color and texture.
How can I make my curtains blackout?
Hang a blackout liner behind them, sew in a blackout lining, or add a blackout shade inside the window frame. Then close the gaps: raise and widen the rod, close the center and hang the curtains to the floor.
Are blackout curtains better than blinds?
Neither is better everywhere. An inside-mount blackout shade leaves narrow gaps at its edges. Curtains leave wider gaps, but they cover the frame and wall. A shade inside the frame with curtains outside it gives the darkest result.
Do blackout curtains have to be black?
No. The opaque lining or core blocks the light, so blackout curtains also come in ivory, beige, sage, grey and other light colors. From outside, you see the back of the curtain. That is the lining or coating, or on a triple weave, the face color.
Can linen, cotton or jacquard curtains be blackout?
Only with a blackout layer. On its own, a linen, cotton or jacquard face usually lets some light through. A blackout lining or backing behind it is what stops the light. At Ona, "linen texture" describes how the face fabric looks, not its fiber.
Are blackout curtains the same as thermal curtains?
Not always. Blackout is about light and thermal is about heat, though many curtains are sold as both. Ona's styles are listed as thermal insulating, and there is no insulation rating.
Are blackout curtains heavy?
Lined blackout curtains are heavier than unlined curtains of the same size, because of the extra layer. Use a rod that can take the weight, follow the maker's load limits and add a center support on long spans.
Blackout curtains or a sleep mask?
A mask darkens only your eyes. Blackout curtains darken the room for everyone in it and add privacy. A mask costs less and travels with you. Curtains need a good fit to work well.
Can you wash blackout curtains?
Often, but follow the sewn-in care label. Coated backings are often marked for a cool, gentle wash with little or no heat, because heat and abrasion can damage the coating. For every Ona style, follow the sewn-in care label.
How this guide was written
- Ona product facts come from the live store and from the specifications shown on each product page, checked on October 16, 2026. "100% blackout" and "thermal insulating" are listed fabric specs. Ona has not tested them independently.
- Fit numbers (fullness, rod height and hem finishes) come from Ona's measuring guide and curtain calculator. The side overhang is a general rule of thumb.
- Construction terms (coated, 3-pass, triple weave and lined) follow common drapery usage. Performance varies by maker.
- Cord safety comes from the U.S. Consumer Product Safety Commission's October 2022 release.
- Images. Room images on Ona are styling visualizations, not light tests. If Ona tests samples, this guide will be updated with the method and the results.