The LHC Short Straight Section (SSS) cryostat houses and thermally protects in vacuum the cold mass which contains a twin-aperture superconducting quadrupole magnet and superconducting corrector magnets operating at 1.9 K in superfluid helium. In addition to mechanical requirements, the cryostat is designed to minimize the heat in-leak from the ambient temperature to the cold mass. Mechanical components linking the cold mass to the vacuum vessel such as support posts and an insulation vacuum barrier are designed to have minimum heat conductivity with efficient thermalisations for heat interception. Heat in-leak by radiation is reduced by employing multilayer insulation wrapped around the cold mass and an actively cooled aluminium thermal shield. The recent commissioning and operation of two SSS prototypes in the LHC Test String 2 have given a first experimental validation of the thermal performance of the SSS cryostat in nominal operating conditions. Temperature sensors mounted in critical locations provide a temperature mapping which allows a crosscheck with the calculated temperature values and thermal performance. Moreover the measurements allowed a validation of the efficiency of the employed thermalisations. This paper presents the experimental results for the thermal performance of cryostat components and gives a first comparison with the design values
