Sandwich covers for microtiter plates: prevent (cross)-contamination even during vigorous shaking permit a reproducible and defined exchange rate of headspace air limit evaporation. Equal physical conditions in all wells is a further requirement: the wells in the corners should have exactly the same characteristics as the wells in the centre of the microtiter plate. The first prototypes of such covers were developped at the ETH Zurich at the end of the 1990s, and have been in use in hundreds of research groups around the world since. The working mechanism is further explained on the page: “Sandwich covers: general principle” Lists of the various sandwich (and their specifications) can be found on: Sandwich covers for 6-well MTPs Sandwich covers for 24-well MTPs Sandwich covers for 96-well MTPs Other sandwich covers (48-well MTPs)