Plastic theatre is a concept introduced by playwright Tennesee Williams in The Glass Menagerie. Williams argues against a one-hundred percent realistic presentation of realistic mise en scene, acting, and other effects on-stage, comparing such technique to a photograph. For him, realism is not the ultimate purpose of art, which can work with or without a realistic approach:
Expressionism and all other unconventional techniques in drama have only one valid aim, and that is a closer approach to the truth. When a play employs unconventional techniques, it is not, or certainly shouldn't be, trying to escape its responsibility of dealing with reality, or interpreting experience, but is actually or should be attempting to find a closer approach, a more penetrating and vivid expression of things as they are.
Williams continues to claim that his conception of "a new, plastic theatre" must supplant realism for realism's sake to reclaim theater's "vitality as a part of our culture." In effect, Williams is arguing that more atmospheric and symbolic effects make the emotion of the play more vivid for the audience.
Williams employs several such plastic theatre techniques in The Glass Menagerie. Music is employed both diegetically and non-diegetically (that is, sometimes the music is playing within the scene itself, with the characters able to hear it, and other times, not) to enhance mood. For example, the theme titled "The Glass Menagerie" is a non-diegetic piece associated with Laura's gentle nature.
The lighting is also unrealistic. Williams calls for dim lighting to evoke the sense of memory—that is, the action onstage is Tom's remembering them and not meant to be a documentary-like presentation of his history. Shafts of light are sometimes cast upon the characters to single them out. Williams points out that the lightning on Laura should be clear and bright, resembling medieval paintings of female saints to emphasize her purity and how precious she is to her brother.
Altogether, the effect of plastic theatre techniques in The Glass Menagerie is expressionist, projecting the inner states of the characters into the physical space they inhabit. This approach works for this story of memory and loss because Tom's recollection of these events are colored by his own emotions. He is not seeing the world clearly and therefore neither will the audience.