The Biopack facility for experimenters working in the field of space biology offers a compact self-standing unit with the following main sub-systems: An incubator for the execution of biological experiments in standard ESA experiment containers (further referred to as EC's) in a micro-gravity or artificial gravity environment. A Freezer-Cooler for storage of EC's before and / or after the experiment. An Electronic Subsystem for housekeeping and experiment data retrieval and control. A main frame (the BIF) interfacing the carrier structure (US Space Shuttle or Space Station) with crew interfaces. The BIF provides the BEI with power and cooling air and harbours the Biopack computer. This paper describes the thermal design of the thermal control unit, housed in the so called BEI (Biopack Experiment Insert), which is a late access item. The BEI harbours the Biopack Experiment Tray (BIT) on which the EC's in the incubator are placed.Reference 1 provides more details on the science related functionality of Biopack.