The shade fabric itself blocks essentially 100 percent of light, but a small amount can still leak around the edges where the shade meets the window frame. The fabric makes the room dramatically darker; to reach true total darkness, the mount and fit matter as much as the fabric, as explained below.

Yes. Blackout shades are the top choice for anyone who needs to sleep when it is light outside, including babies, kids, and night-shift workers, because blocking outdoor light supports deeper, longer sleep. For a baby's room, see our guide to blackout curtains for a nursery. The fabric itself blocks the light, but a little can still leak around the edges, since the gaps come from the space between the shade and the frame, not the fabric. To get true darkness, choose an outside mount that extends a few inches beyond the window on all sides, or add side channels or tracks for an inside mount; mounting the shade higher and wider and adding a valance also helps seal the top and sides. Cordless options add child safety.

Blackout shades are made to block essentially all light for a fully dark room, while room-darkening shades cut most light but still let a soft glow through, leaving the room dim rather than pitch black. Choose blackout for nurseries, bedrooms, and media rooms where you want total darkness, and room-darkening when you want to reduce light and glare but do not need complete blackout.

Yes. By blocking direct sunlight, blackout shades reduce solar heat gain in summer and help hold warmth in winter, easing the load on your heating and cooling. For the strongest insulation, choose blackout cellular (honeycomb) shades, whose air pockets add a thermal barrier at the window.

They help a little. The dense, heavier blackout fabric absorbs some sound and can slightly soften outside noise, but shades are not a true soundproofing solution. For a bigger difference, layer them with curtains or choose cellular blackout shades, whose air pockets dampen sound a bit more.