Most curtains marketed as 'blackout' do reduce light, but very few make a room properly dark. The difference between 'dim enough to nap' and 'I have no idea what time it is' comes down to four things: the fabric, the header type, the size, and how you hang them.

1. Fabric – the actual blackout layer

True blackout curtains have a tightly woven outer fabric backed by a coated lining. The lining is what does the work – it's a layer of acrylic or similar that prevents light passing through the weave. Curtains marketed as 'thermal blackout' add an additional insulating layer for warmth and noise reduction.

Crushed velvet is a popular blackout face fabric in the UK because the high-pile texture catches the light beautifully on the room side, while the dense weight on the back stops light bleeding through. The SAIMAZ crushed velvet curtains range uses this construction.

2. Header type: eyelet vs pencil pleat vs tab top

• Eyelet (ring top) – metal rings sit on a pole. Easiest to hang, easiest to slide, and the rings sit close to the pole so the top of the curtain stays flush – less light leakage at the top edge.
• Pencil pleat – gathered tape with a more traditional, formal look. Hangs from hooks. More fabric per metre means more drape, but slightly more light can leak around the edges.
• Tab top – fabric loops over the pole. Less common in blackout designs because the loops naturally let light through.

For maximum darkness, eyelet on a wall-mounted pole gives the cleanest seal.

3. Size them generously

This is where most rooms lose the war on light. The single biggest mistake is buying curtains exactly the width of the window. Light leaks around the sides.

• Width: aim for the curtain (closed) to be 1.5–2× the window width, so the gathers stack up at the edges and overlap when shut.
• Drop (length): for a 'puddle' effect on the floor, allow 5–10 cm extra. For sill-length, measure to 1 cm above the sill so they don't catch on radiators.
• Pole position: mount the pole 15–20 cm above the window frame and extend it 15–20 cm past each side of the window. This way, when curtains are closed, no part of the window is uncovered.

4. Plug the gaps

Even good blackout curtains let small amounts of light through three places: the top, the sides, and the gap between two panels. Fix each one:

• Top gap: use a ceiling-mounted track or a pelmet, or extend the pole away from the wall by 8–10 cm so the curtain falls in front of the window frame, not flush against it.
• Side gap: always size the pole wider than the window. Some shoppers add stick-on light-blocker strips at the wall edge – fiddly but effective in a bedroom.
• Centre gap: when fully closed, two panels should overlap by 15–20 cm in the middle. Standard pairs are sized for this, but only if you bought the right width.

How dark is 'blackout'?

Properly hung blackout curtains can reduce light entering a room by up to ~99%. They're rarely 100% dark – some light always finds the smallest gap at the rod – but they're more than enough for shift workers, daytime sleepers, light-sensitive children, or anyone with a TV in the bedroom.

Bedroom, living room and home cinema picks

• Bedroom: crushed velvet eyelet pairs in deep tones (black, charcoal, navy). Adds warmth and noise dampening too.
• Living room: lighter colours (silver, beige, pewter) still block light when lined; the velvet finish catches lamp light beautifully in the evening.
• Home cinema / TV room: oversize them. Go 30–40% wider than the window to absorb screen reflections.

Browse the SAIMAZ blackout curtains collection – crushed velvet, eyelet, thermal-insulated, in multiple sizes and colours, with free UK delivery.