Fix it
Blackout Curtains Not Blocking Light? Fixes That Work
Light leaking around the edges, glowing through the fabric, or curtains that will not stay closed? Diagnoses and fixes.
When blackout curtains disappoint, the fabric is rarely the problem. Nine times out of ten it is coverage: light sneaking around the panel edges, not through the weave. Here is how to find and fix the actual leak.
Light leaks in around the top, sides, or bottom
Remount wider and higher. Move the rod 4 to 6 inches above the frame and extend it 3 to 4 inches past each side so the panels cover wall around the window. Switch to a wraparound rod so the panel ends return to the wall. For the bottom gap, longer panels that touch the floor seal it. Edge leaks are an installation problem with an installation fix.
Light glows through the fabric itself
The fabric is not true blackout: either a coated curtain whose backing has degraded, or a room-darkening panel mistaken for blackout. Hold the fabric to a bright light: if light passes through the weave, no mounting trick fixes it. Replace with triple-weave blackout panels in a dark color.
Light comes through the middle where panels meet
Overlap the panels by several inches at the center instead of just meeting them. Magnetic curtain tiebacks or sew-in magnets hold the overlap closed. Alternatively, order panels with extra width so the center overlap is generous even when drawn.
Curtains will not stay closed or keep sliding open
Heavy blackout panels slide on smooth rods. Add a center bracket or a small hook that holds the leading edges together. For grommet panels, a magnetic tieback at the center works. Check that the rod is level: even a slight slope lets heavy panels migrate downhill overnight.
Questions, answered
My curtains worked at first, then started letting light through. Why?
Coated blackout curtains degrade: the sprayed backing cracks at fold lines and peels over time, especially after washing. Triple-weave curtains do not have this failure mode. If light is coming through the fabric where it did not before, the coating has failed and the panels need replacing.
Can I make existing curtains more blackout?
Add a blackout liner behind them, or layer a blackout shade inside the window frame. Remounting the rod wider and higher also helps any curtain. But a liner behind a sheer curtain still leaks at the edges: manage expectations.