Blackout Windows
A blackout fabric blocks light through the fabric. It does nothing about the gap around it. This page explains where the remaining light comes from and the two levels of fix — a shade running in side rails, or a fully enclosed window.
Shop Blackout Windows
Made to your exact window size. Prices shown for a 36" × 60" window — your size is priced live in the next step.
Quick answers
Will a blackout blind make the room completely dark?
On its own, no. The fabric stops light passing through it, but an inside-mount shade has to be cut narrower than the opening to move freely, so a gap remains down each side. In a bedroom at night that is usually fine. For a nursery at nap time, a night-shift sleeper or a projector room, it is the gap — not the fabric — that you need to deal with, and that means side rails or a fully enclosed window.
What are side rails, and what do they actually do?
Side rails (also called side channels or U-channels) are aluminium tracks fixed to the window jamb on each side. The fabric edge runs inside the track rather than beside it, so the side gap is covered rather than merely narrowed. They are the single most effective thing you can add to a blackout shade, and on our shades they are a $100 option.
What is a fully enclosed window?
All three gaps closed at once: side rails down both jambs, an enclosed cassette headrail that boxes in the roll so light cannot pass over the top, and a bottom rail that seats into the channel or against the sill. It is the closest a retrofit shade gets to a darkroom, and it is what we would specify for a nursery, a shift worker's bedroom or a home cinema.
Why a blackout blind still lets light in
“Blackout” describes the fabric, not the window. A blackout fabric is coated or foam-backed so that effectively no light passes through the cloth itself. Hold a piece up to a lamp and you see nothing. Put it on a window and you will still see light — because the light is not coming through the fabric. It is coming around it.
An inside-mount shade has to be cut a little narrower than the opening, or it would scrape the jambs and jam. That clearance is typically a quarter to half an inch on each side. At night you would never notice it. At seven in the morning in June it is two bright vertical lines, and in a nursery that is the difference between a child sleeping until seven and waking at five.
So the useful question is never “is this fabric blackout?” — most of ours are. It is which gaps are you closing, and how far do you need to go.
Three levels of dark
Most rooms only need the first or second. Go to the third when someone has to sleep while the sun is up.
Blackout fabric, standard fit
A coated or foam-backed blackout fabric on an ordinary inside-mount shade.
- Stops
- All the light that would pass through the fabric.
- Still lets through
- A soft halo down both sides, and light over the roll on an open-roll shade.
- Right for
- Bedrooms where you sleep at night and just want the streetlight and the early sun knocked back.
The fabric choice only — no extra hardware.
Blinds with side rails
The same shade, with aluminium U-channels down both jambs. The fabric edge runs inside the channel.
- Stops
- The side gaps, which is where most of the remaining light was coming from.
- Still lets through
- A little light over the roll unless the headrail is enclosed, and a thin line under the hem.
- Right for
- Nurseries, shift workers, anyone who sleeps when it is light outside.
Side rails are a $100 option, up to a 110" drop.
A fully enclosed window
Side rails, plus an enclosed metal cassette that boxes in the roll, plus a bottom rail that seats into the channel or against the sill.
- Stops
- Sides, top and bottom together — every path except the fabric itself, which the blackout fabric already handles.
- Still lets through
- Very little. This is as dark as a retrofit shade gets.
- Right for
- Home cinema, a baby who wakes at first light, a bedroom you sleep in during the day.
Rails plus the enclosed cassette headrail, both priced in the configurator.
Blinds with side rails, in detail
A side rail is an aluminium U-channel screwed to the window jamb. The shade is made narrower than usual on purpose, and its edges sit inside the two channels. Light that would have run down the side gap now meets the back of an aluminium extrusion.
- They are specified, not retrofitted. The shade is cut to the channels, so rails are chosen when the shade is made.
- They need a flat jamb. The channel has to sit against something. A deep, square reveal is ideal; a rounded or tiled return may need packing.
- There is a height limit of 110 inches. The channel is a rigid extrusion cut to the drop; above 110" the option is unavailable and the configurator greys it out.
- They slightly change how the shade moves. A shade in channels runs with a little friction, which is normal and is what keeps the edge sealed.
On our shades this is the Side Channels option, currently $100, available on eleven of our ranges including the blackout roller. If you only ever add one thing to a blackout shade, add this.
See blackout roller shades with side channels →A fully enclosed window
Rails deal with the sides. A fully enclosed window deals with all three paths at once, and it is the specification to ask for when the room has to be properly dark in daylight.
1. Side rails on both jambs
Closes the vertical gaps, as above.
2. An enclosed cassette headrail
An open-roll shade leaves the top of the roll exposed, so light passes over the tube and down the face of the fabric. A fully enclosed cassette boxes the roll in on all sides, with the fabric leaving through a narrow slot. In the configurator this is the metal cassette valance rather than an open or fabric-wrapped one.
3. A seated bottom rail
The bottom bar finishes inside the channels and closes against the sill, so the strip of light under the hem closes as the shade reaches the bottom.
The result is not a laboratory darkroom — it is a window covering, and a determined beam will find a badly out-of-square reveal. But in a normal room it is the difference between reading by the light coming around your shade and not being able to see your hand.
Which one does your room need?
| The room | What we would fit |
|---|---|
| Adult bedroom, sleeps at night | Blackout fabric on its own. Add rails only if the streetlight is right outside. |
| Nursery or a toddler waking at dawn | Blackout fabric in side rails. This is the common case and the one rails were made for. |
| Night-shift worker sleeping in the day | Fully enclosed: rails, enclosed cassette, seated bottom rail. |
| Home cinema or projector room | Fully enclosed, and consider an outside mount so the shade overlaps the wall as well. |
| Living room, glare on a screen | Blackout is usually the wrong tool. A solar shade cuts glare without making the room a cave. |
| Rental you cannot drill into | Blackout fabric, outside mount where the fixings allow. Rails need screws into the jamb. |
Not sure which applies? A free design consultation is the fastest way to get this right the first time.
Where the light actually gets in
Down the sides
An inside-mount shade is cut narrower than the opening so it can move. That ¼ to ½ inch gap on each side is the single biggest source of light in a blackout room.
Over the roll
On an open-roll shade the fabric leaves the tube at the back, so light passes over the top of the roll and down the face of the shade.
Under the hem
The bottom bar sits a little above the sill. On a bright morning that line reads as a bright strip across the floor.
Through the fabric
Only this one is the fabric's job. A true blackout fabric is coated or foam-backed, so effectively nothing passes through it.
Frequently Asked Questions
Blackout, answered honestly
Will a blackout blind make the room completely dark?
On its own, no. The fabric stops light passing through it, but an inside-mount shade has to be cut narrower than the opening to move freely, so a gap remains down each side. In a bedroom at night that is usually fine. For a nursery at nap time, a night-shift sleeper or a projector room, it is the gap — not the fabric — that you need to deal with, and that means side rails or a fully enclosed window.
What are side rails, and what do they actually do?
Side rails (also called side channels or U-channels) are aluminium tracks fixed to the window jamb on each side. The fabric edge runs inside the track rather than beside it, so the side gap is covered rather than merely narrowed. They are the single most effective thing you can add to a blackout shade, and on our shades they are a $100 option.
What is a fully enclosed window?
All three gaps closed at once: side rails down both jambs, an enclosed cassette headrail that boxes in the roll so light cannot pass over the top, and a bottom rail that seats into the channel or against the sill. It is the closest a retrofit shade gets to a darkroom, and it is what we would specify for a nursery, a shift worker's bedroom or a home cinema.
Can I add side rails to a shade I already own?
Usually not well. The channels have to be sized to the shade and the shade cut to the channels — retrofitting them to an existing shade normally leaves the fabric too narrow or binding in the track. Rails are specified when the shade is made, which is why they appear in the configurator rather than as an accessory.
Is there a height limit on side rails?
Yes. The channel is a rigid extrusion cut to the drop, and the maximum we can supply is 110 inches. Above that the option is greyed out in the configurator. The shade itself can go taller; the rails cannot.
Does an outside mount solve the gap instead?
Partly, and it is the cheapest route. Mounting outside the opening and overlapping the wall by two or three inches on each side hides the side gap without any rails. You still get light over the roll unless you add an enclosed cassette, and it changes how the window looks. Where an outside mount suits the room, it is a sensible middle option.
Do blackout cellular shades work the same way?
The fabric does — a blackout cellular has an internal foil liner. The gaps behave the same, but cellular shades run on a different track system, so where total darkness matters we normally recommend a blackout roller in side rails rather than a cellular.
Does a darker fabric make a darker room?
No, and this trips people up. Blackout is a construction, not a colour: a white blackout fabric with a foam backing blocks just as much as a charcoal one. Colour changes how much light bounces back into the room and how the shade looks from the street, not how much gets through.
Price a genuinely dark window
Enter your size, choose a blackout fabric, then add side rails and an enclosed cassette. The price updates as you go.