A blindfold is a covering for the eyes which prevents the wearer from seeing. This is often regarded as an essential part of bondage for inducing a sense of helplessness in the bound victim, making escape more difficult and its visual impact on the captor and bystanders.
Blindfolds can range from simple cloth bands tied around the head to complex leather head harnesses which buckle around the head and neck. In SM play, blindfolds enhance the loss of control felt by the bottom and allows the top much greater control over what the bottom can experience.
It may be possible for even a bound person to remove the blindfold by rubbing his or her head against the floor or another object. The blindfold can be secured by tape or by being part of a head harness. Hoods are often far more dificult to remove.
It is difficult to ensure that a blindfold is completely light-tight, especially in the corners of the eyes by the nose. A heavily padded leather blindfold often works well, or the blindfold can be augmented by sticky tape or by putting blobs of something soft over the eyes before applying the blindfold (ensuring that it is something that cannot damage or irritate the eyes).
Hoods may be used, though if they are made of cloth, even darlex, there may be some see-through, and with a leather or rubber hood some light may get in through the air-holes. A blindfold covered by a hood can be very effective.
Another technique is to have a wide blindfold with a hole for the nose. The hole needs to be an appropriate size to fit the nose of the victim.