A blackout roller blind is a coated polyester panel that passes no light through the cloth itself. In a Dhaka bedroom that faces west, it is the difference between waking at six and sleeping until you choose to. The same property makes it the standard answer for a media room, a night-shift worker's room, or a nursery where an afternoon nap has to survive full sun.

Bear one thing in mind: blackout describes the fabric, not the fitting. Mounted inside the reveal, a few millimetres of clearance on each side let the blind move, and daylight will find that gap. Mounted outside the frame with a two to three inch overlap, the room genuinely goes dark. Tell us which you want before we measure.