ETFE film is dimensionally stable so by use of a methods and machines which utilise that stability structures can be made by initial slight tension for retention upon a skeletal frame typical of a greenhouse a convenient manner of achieving such structures is provided despite the flaccid nature of such ETFE film. A consistent film overlap (15) can be forced into spaced channels (11) with a profile element (10) to provide an initial lateral tension to retain the film in a frame. By use of heat shrinkage the tension can be equalised and/or enhanced with heat shrinkage upon cooling after local heating of the film.
