Do eye masks and earplugs improve sleep?

Short answer

For earplugs in a noisy room, yes. Of the 23.4 minutes of deep sleep lost to traffic noise, earplugs recovered 16.9 minutes. At home, an eye mask did not change sleep time or sleep quality, and next-day reaction speed and word-learning scores were better.

Do eye masks and earplugs improve sleep?
'Block light and sound → deeper sleep': is it true?
Many say you sleep more soundly with an eye mask and earplugs. If so, what part of sleep changes? We checked noise, light, and eye masks at home, in that order.
On noisy nights, earplugs worked
They recovered 16.9 of the 23.4 minutes of deep sleep lost
25 people slept 7 nights in a sleep lab. Playing plane, car, and helicopter sounds cut the deepest sleep by 23.4 minutes compared with a quiet night. Foam earplugs, which lowered sound by 25.5 dB (decibels, a unit of loudness) on average, brought back 16.9 minutes, and sleep structure showed no difference from a quiet night.
But very loud sounds got through
At the loudest level the protection broke down
In the same study, with earplugs, sounds up to 55 dB showed no difference from a quiet night. At the loudest 65 dB sounds, waking increased and deep sleep dropped. A steady background sound played to cover the noise (pink noise) actually cut dreaming sleep (REM sleep) and reduced awakenings less than earplugs.
With both light and sound
Using an eye mask and earplugs together meant less waking
40 people slept in a room recreating the noise and lights of a hospital intensive care unit. Those using an eye mask and earplugs woke less and fell asleep faster, but total sleep time did not increase. An analysis that pooled 797 people in intensive care units found self-rated sleep quality improved with an eye mask alone or both together, while earplugs alone made no difference.
So what about an eye mask at home?
Sleep time stayed the same
94 people slept at home in summer, when the sun rises early, wearing a light-blocking eye mask for 1 week and a fake mask that let light in for 1 week. Sleep time was 8.24 and 8.26 hours, with no difference. Self-rated sleep quality showed no difference either, and sleep stages in 35 people showed no difference.
The difference showed up the next day
Reactions were 0.006 seconds faster and learning scores were higher
In the same study, in the eye mask week, next-day reaction time was 0.310 seconds, faster than 0.316 seconds in the fake mask week. Scores for learning word pairs were also higher, 65.06 vs 63.87. People whose learning scores rose more in the mask week spent more time in deep sleep on mask nights.
Summary: they help when there is light or sound to block
Deep sleep and the next day changed more than sleep time
Earplugs recovered deep sleep on noisy nights, but did not fully block very loud sounds. At home, an eye mask did not lengthen sleep and made next-day reactions and memory slightly better. In a room with street noise or early morning light, trying an eye mask and foam earplugs works.