A mask makes the room dark when you cannot: a bright street light, a partner on a phone, a nap in the afternoon. Comfort comes first, because you will only wear a mask that you forget is there.
Mulberry silk eye mask
Smooth and light on the skin around the eyes.
Look for
Silk on both sides, or at least on the side that touches your face.
A soft filling (silk or cotton) that blocks light.
A wide, soft strap, or an adjustable one that does not pull hair.
A seller who says how to wash it.
Skip it if you wear lash extensions. A contoured mask keeps fabric off the lashes.