Cages are some of the largest items of bondage equipment, and provide a 'space' of confinement rather than directly controlling the freedom of the limbs. Unlike enclosed spaces such as cells, sleep sacks or body bags, cages also display the captive, in their vulnerability, making them more arousing for many people, including those who would consider themselves vanilla - for example, cages are often used to contain dancing girls in nightclubs.
Cages for use in bondage scenes are typically constructed of wire mesh, or steel tubing or bars. (Wire cages can be bought cheaply from pet shops, but do not provide the feeling of inescapability that many captives seek.) One of the important uses of cages is to provoke feelings of psychological reactance as the captive struggles against the bars, and then reaches the state of helplessness once convinced of their inescapability.
There are three basic designs of cage
Puppy cage: This is probably the most common cage design seen in clubs and dungeons. Typically, they are about 4 feet long, 2-3 feet wide and about 3 feet tall. The dimensions give the captive little room for movement and force them to kneel or lie curled up. Most commercially available cages can be dismantled for storage.
Upright cage: is designed to confine a person in the standing position, typically they are about 2 feet wide, 1-2 feet in depth and about 7 feet high. Designs usually incorporate multiple doors to allow the prisoner access to the captive's breasts and genitals without having to release them.
Gibbet cage: A gibbet cage is based on the historical device used for displaying the bodies of executed prisoners. (It should be noted that gibbets were never designed to imprison the living!) The SM community has taken the concept and transformed it into a cage roughly in the shape of a person, designed for extremely restrictive confinement. Gibbet cages look extreme and provide an environment where the captive is almost totally immobile and very helpless. The main disadvantage of this type of cage is that the person being confined needs to be approximately the same size as the cage. Very tall people will just not fit and very short people will risk looking slightly ridiculous. Since movement can be severely restricted, no-one should be left in a gibbet cage for long, as discomfort can quickly and suddenly arise arise, with the potential for physical harm to soon follow.
A small number of manufacturers (www.permanentbondage.com was one such although it appears no longer to be trading) have taken the concept of the gibbet cage to its logical conclusion and produce cages which precisely follow the contours of the human body. These are usually custom built for the subject and can be very expensive.