100% Blackout Curtains: How to Get Total Darkness

Why a “blackout” curtain often still lets light through

A curtain labelled “blackout” is not necessarily a 100% blackout. Many block direct light but leave a residual halo, for two reasons.

First the fabric: too thin, too loosely woven or without a dense layer, it lets daylight filter through. Second, and this is the most common, the leaks at the edges. Light gets around the curtain at the sides, over the top above the rod, and at the bottom if the curtain stops too short. A 100% blackout fabric hung badly leaves a room far from complete darkness. The full diagnosis of light leaks is in our article on light coming in at the sides of the curtain.

What makes a true 100% blackout

A true 100% blackout comes down to fabric construction, not colour. 100% is achieved with a single dense layer, or with several technical layers including a blackout membrane.

Colour does not determine blackout: a light fabric built correctly blocks as much as a dark one. We cover this in detail in our article on the white blackout curtain. For complete darkness, Kurtens offers a 100% blackout, in several colours and fabrics.

Decoding the levels of blackout

Not all curtains that “darken” are equal. Here is how to place what you are buying.

The term “blackout” does not, on its own, guarantee 100%. A light-filtering curtain filters light without being blackout. For the difference between blackout, light-filtering and opaque, see our comparison of blackout, light-filtering and opaque.

Kurtens offers a light-filtering curtain and two 100% blackout ranges made-to-measure, in several fabrics, colours and styles, to match the blackout to each room.

Achieving complete darkness: fabric is not enough

A 100% blackout fabric only delivers complete darkness with no light leaks. Three rules:

• Cover wide: the rod extends 15 cm beyond each side of the window, and the curtain reaches the floor.
• Mount high: fit the rod about 15 cm above the window, or fix it to the ceiling with a curtain that reaches the floor, to limit light at the top.
• Go made-to-measure: a curtain sized from the rod, not the glass, reduces the side gaps that standard sizes often leave. Hanging does the rest.

Simple test: close the curtain in broad daylight and look for a halo around the edges. If there is one, the problem almost always comes from the fit or the dimensions, not the fabric.

Which rooms 100% changes everything for

100% blackout is not just a comfort. In some rooms, it is the only level that gives complete darkness.

• Bedroom: complete darkness keeps the room dark in summer, when daylight comes early.
• Baby's or child's room: to darken the room for naps or a bedtime before nightfall, choose a 100% blackout fabric.
• Night work: for a dark bedroom in broad daylight, choose a 100% blackout fabric and remove the light gaps around the curtain.
• Home cinema: a dark room matters more than an expensive projector, as we explain for the home cinema curtain.

Does a blackout curtain block 100% of light?

Not necessarily. A curtain sold as “blackout” can let a halo filter through the fabric; only a 100% blackout fabric stops all the light that hits it. And even that fabric will not make a room dark if the curtain is too small: daylight then gets in at the sides, the top and the bottom.

On a product page, check that the blackout is stated as 100%. The table of levels above places the other labels. At Kurtens, the single-layer blackout curtain and the 3-in-1 blackout, thermal and acoustic curtain are both 100% blackout: what remains is size and hanging, covered in the next sections.

Do blackout curtains work, and which ones make a room truly dark?

Yes against direct light: every blackout curtain darkens a room noticeably. Only those stated as 100% blackout give complete darkness, provided no light gets around the curtain. At Kurtens, these are the single-layer blackout curtain, thin and fluid, and the 3-in-1, which adds thermal and acoustic insulation. The colour of the fabric makes no difference.

• Single-layer blackout: 100% blackout and 100% UV-blocking in a single 315 g/m² layer, reversible.
• 3-in-1 blackout, thermal and acoustic: three technical layers, 620 g/m², for complete darkness plus thermal and acoustic insulation.

The 3-in-1 weighs about twice as much per square metre. On a large window it needs a wall fixing: it is not compatible with a telescopic rod. Choosing the support is covered in our article on the rod for heavy curtains.

How do you black out a window for the night?

Choose a 100% blackout curtain and make it larger than the window. The rod goes about 15 cm above the opening and extends 15 cm beyond each side. The curtain reaches the floor. Its total flat width is 2 to 2.5 times the width of the rod. Closed, it covers the whole window frame.

• Rod length: window width plus 15 cm on each side. A 200 cm window needs a 230 cm rod. If no rod is fitted yet, add these 30 cm to the window width.
• Curtain width: 2 to 2.5 times the rod, so 460 to 575 cm for a 230 cm rod. For two panels, divide by two. In the configurator, enter the flat width of each panel.
• Height: for a curtain that reaches the floor, measure according to the heading chosen in the configurator. Kurtens makes each curtain to the dimensions you enter.

A shutter or blind already in place is still useful: the 100% blackout curtain stops what still gets through its slats or gaps.

How do you make a bedroom completely dark with blackout curtains?

Deal with every way light gets into the bedroom, not just the fabric. A 100% blackout curtain sized wide, panels that meet without a gap in the centre, no light above the rod, a hem that touches the floor. Then close the curtains in broad daylight and check the sides, the top, the bottom and where the panels meet.

• The centre: with two panels, split the total width calculated above between them, then check that they meet without letting light through. A single panel removes this join.
• Every window: one poorly covered window is enough to light the room. Apply the same sizing and hanging rules to all of them.
• Standby lights: in a truly dark bedroom, the standby lights of devices become visible. Switch them off or cover them.

Frequently asked questions

For the right level of blackout at your dimensions, explore Kurtens made-to-measure blackout curtains, 100% blackout, in several fabrics and colours, made to your dimensions.