Abstract: A framework cassette of thin sheet intended to be joined to adjacent cassettes so as to constitute a lost form when casting concrete framework and co-operating with the concrete in the finished framework as regards the absorption of forces. It consists of a rectangular bottom (11) along the two longitudinal sides of which edge beam sections are bent up. These edge beam sections consist in part of an upper, horizontal flange (5), a vertical web (3) with bulges (8) and furthest down a sleeve (6). On the sleeves (6) and between them is located a top section (9) which is also secured to them. The space between the top section (9) and bottom (11) of the cassette can be filled with insulation or used for installation material (14). The concrete is cast over the top section (9) and between the webs (3).