Blackout vs room-darkening vs sheer
Blackout blocks ~99% of light (usually a 3-pass coated or triple-weave fabric); room-darkening blocks 70–90%; sheers only diffuse.
Why it matters
Only true blackout gets a west-facing bedroom dark enough for day sleep or a baby's nap.
What to check
Light leaks around the edges — the rod must extend 15–20 cm beyond the window on each side.