[1] Their stories feature imprisoned women who are subjected to sexual and physical abuse, typically by sadistic male or female prison wardens, guards and other inmates.
[2] The flexible format, and the loosening of film censorship laws in the 1960s, allowed filmmakers to depict more extreme fetishes, such as voyeurism (strip searches, group shower scenes, catfights), sexual fantasies (lesbian sex, rape, sexual slavery), fetishism (bondage, whipping, degradation), and sadism (beatings, torture, cruelty).
Prior to these films, another expression of pornographic women in prison was found in "true adventure" men's magazines such as Argosy in the 1950s and 1960s, although it is possible that Denis Diderot's novel The Nun anticipated the genre.
Occasionally a new inmate is an undercover reporter investigating corruption as in Bare Behind Bars or a government agent sent to rescue a political prisoner (Caged Heat 2: Stripped of Freedom, Love Camp 7).
Most commonly, the prisoner is reunited with a man (a lover, father, or priest) who guides her to goodness so she can reestablish her life with familial and heterosexual relationships.
But it was not until the 1930s that Hollywood began making movies partially set in women's prisons, such as Up the River (1930), with Claire Luce, Ladies They Talk About (1933), with Barbara Stanwyck, Hold Your Man (1933), with Jean Harlow, and Girls on Probation (1938), with Jane Bryan, but generally, only a small part of the action took place inside the institution.
It was not until the 1950s, beginning with the release of Caged (1950), starring Eleanor Parker and Agnes Moorehead, So Young, So Bad (also 1950), with Anne Francis and Rita Moreno, Women's Prison (1955) with Ida Lupino and Cleo Moore and, in Great Britain, The Weak and the Wicked (1954), with Glynis Johns and Diana Dors, that an entire film was set inside a women's correctional facility.
Mainstream, non-exploitation prison films dealing with this theme include Bangkok Hilton (1989) starring Nicole Kidman and Brokedown Palace (1999) with Claire Danes, both which are set in Thailand and are focused on women who are imprisoned for smuggling drugs.
Jonathan Demme's Caged Heat (1974) is one of the better known WiP films and has a cult following due to its tongue-in-cheek approach and casting of horror icon Barbara Steele as the warden.
The abuse of Chinese women in Japanese detention or prisoner-of-war camps during World War II is depicted in a series of Hong Kong films.
The topic of sex "is usually considered taboo in traditional Chinese society", which makes the film industry scandalous and frowned upon by many.
One of the very early examples of the genre in Japan began with Death row Woman, a noir drama made by the master of J-horror Nobuo Nakagawa in 1960, although the plot doesn't focus entirely inside of the prison.
Many Japanese films include themes of vengeance and retribution with a heroine who take revenge against the drug or prostitution syndicates responsible for her incarceration.
The "jungle prison" subgenre has films set in fictional Banana republic nations run by corrupt dictators in either South America or Southeast Asia.
These films usually involve a revolution subplot with political prisoners freed by other inmates in a climactic raid where the villains are killed.
Sweet Sugar (1972) starred Phyllis Davis, Caged Heat 2: Stripped of Freedom (1994) featured Jewel Shepard as an undercover agent.
Jesus Franco's Sadomania features scenes such as gladiator fights to the death and prisoners hunted like animals in an alligator-infested swamp.
The stories are set in isolated convents that resemble prisons where sexually repressed nuns are driven to rampant lesbian sex and perversity.
Bars and Stripes is a video producer that maintains a website entirely devoted to its line of prison-based BDSM fetish films.