Abstract : The optimization in thermal performance of cryostats is a must for energy saving in large cryogenic installations such as accelerators. Static loads affect the power needed for the system in some percentage depending on the application. This work’s aim is to understand the optimal temperature at which a typical thermal screen protecting the superconducting devices’ cold mass in a big collider like the Future Circular Collider has to be operated in order to minimize the refrigeration power during operation. The approach is done through energy balance and the minimum power required is calculated in function of the thermal screen temperature. Data on the heat reaching the cold mass (1.8 K), through the MLI (Multilayer Insulation systems), has never been tested extensively for hot boundary temperatures between 20 K and 77 K. Different MLI configurations have been tested also at different levels of degraded vacuum, with residual gas pressures between 10-6 and 10-4 mbar. The experimental work was done by means of a boil off calorimeter specifically designed for MLI tests and modified for this work. The peculiarity of the test set-up is the use of an adjustable temperature aluminium thermal screen (ATS), used as hot emitting surface. The MLI blanket samples are prepared with a specific methodology set up in order to have control on the layers density, a very important parameter influencing the MLI performance.