The invention relates to a piercable hermetic cover (2) for a bioassay cartridge (4) with at least one reaction chamber (6). Characteristic for the invention is that: the cover (2) comprises at least a top layer (8), a middle layer (10), a bottom layer (12), and sites intended for piercing (14); and the cover (2) has, at the sites (16) intended for piercing, a hollow space (18) between the top layer (14) and the bottom layer (12). The present invention also relates to a system (20) comprising a bioassay cartridge (4) and a cover (2) for the cartridge (4). The present invention further relates to use of the cover (2) for covering the cartridge (4).