A study of the first in-orbit temperatures of Huygens shows that the probe will very likely survive thermally all vacuum cruise and coast phases. Calculated heat fluxes, mass flows of Titan's atmosphere into and out of the probe and temperatures give confidence also for the mission phase proper in 2004 i.e. the 2.5 h descent into Titan's -2OO°C atmosphere.Basotect foam bags insulate the probe from this atmosphere. These bags and their fixation had drastically to be modified between Titan test on STPM (May 95) and on FM (June 96). The mission phases, thermal requirements, thermal design, tests with the probe, special tests for the foam bag development and their modification are presented.