Without the use of a heated lid, solvent molecules will evaporate to the gaseous phase during the heating process of a liquid sample and subsequently condensate against the cooler surfaces of lid and container wall. Hence, the volume of the sample is reduced while its concentration increases (fig. A).Sensitive reactions may be influenced by this change in reaction conditions. In the case of very small sample volumes, the condensation process can leave such a small residual sample volume inside the reaction tube that the sample is no longer mixable. Under such conditions the biochemical reaction will be neither optimal nor reproducible.When using the Eppendorf ThermoTop, the surfaces of the tube lids and upper tube walls are warmed in such a way as to prevent the formation of condensation effectively.Thus, sample concentration remains stable, reaction conditions are strictly adhered to, and reproducibility of experiments is improved (fig. B).