Blind fabrics are sold by how much light they let through, usually in four broad levels: blackout, dimout, light-filtering and voile (or sheer). The names describe the fabric, not the finished blind, and that distinction matters - so here is what each one really does, and where it belongs.
Blackout
Blackout fabric is woven tightly or given a coated backing so daylight cannot pass through the cloth itself. It is the choice for bedrooms, nurseries, media rooms and anyone sleeping during the day. The honest caveat is that a blind is not a sealed box: the fabric has to sit slightly narrower than the opening to move, so light always leaks around the edges and along the top, leaving a visible glow even with a good blackout fabric. To get close to true darkness you need to seal the sides - side channels or blackout tracks, a framed style such as perfect-fit, a roof blind held in its channels, or a face fit cut to overlap the reveal. One firm limit: slatted and louvred blinds (venetian, vertical) and layered day-and-night blinds cannot truly black out, because the slat gaps and cord holes always pass light. For them, "blackout" means the darkest the fabric goes, not a dark room.
Dimout
Dimout sits between standard and blackout: it blocks most daylight but not quite all of it. It is a sensible middle ground for a bedroom that does not need to be pitch dark, or a living room you want to shade for a screen without going fully black. It also keeps better night-time privacy than a light-filtering fabric.
Light-filtering
Light-filtering fabric is woven loosely enough to pass soft, diffused daylight but closely enough to screen the view in, so a room stays bright and airy while keeping its privacy through the day. It is ideal for living rooms, kitchens, dining rooms, home offices and north-facing rooms that need all the daylight they can get. The catch is what happens after dark: once it is black outside and your lights are on, the fabric turns partly see-through from the street, so you become a silhouette. For night privacy, pair it with a blackout blind or curtains, or step up to dimout. It is not made for sleep - that is blackout's job.
Voile and sheer
Voile and sheer fabrics are the lightest of all: translucent cloth that softens daylight and adds a decorative, gauzy layer of daytime privacy without really cutting the brightness or the view. They are about look and softness rather than light control, and are often layered with a second blind or curtains that do the blocking.
Choosing by room
- Bedrooms and nurseries: blackout, ideally with side channels or a face fit for the darkest result; dimout if you only want to take the edge off.
- Living rooms, dining rooms and home offices: light-filtering for daytime brightness with privacy, backed by something for the evening if the room faces the street.
- Kitchens and bathrooms: light-filtering or voile for privacy, in a moisture-tolerant fabric such as a PVC-coated roller or an aluminium or faux-wood venetian.
- Studies and rooms with screens: dimout or light-filtering to kill glare without working in the dark.
If a single blind cannot do both jobs - bright by day and private by night - the usual answer is to layer two, such as a voile or light-filtering blind with a blackout blind or curtains behind.