A thermal condition of a pack of screen-vacuum thermal insulation (STI) of spacecrafts (SC) in the sun flux was studied experimentally. The pack consists of facing materials (glass cloth of different colours, fabrics of synthetic materials), sreens from polymer films (mylar, kapton) with one and two-sided metallization with different gasket materials. Experiments were conducted in the simulation thermal vacuum chamber with a solar simulator (So = 1.4 kW/m2).It is demonstrated that there was a significant nonuniform temperature distribution along pack screens - there was a significant overheating (to 150 K depending on pack composition) of internal layers in comparison with external ones. Highly satisfactory results are explained by the greenhouse effects in the STI. The corresponding calculation mathematic model was developed.It is demonstrated and experimentally verified that if the pack construction of STI is not flat, but it is a cavity, then in this case the influence of the received effects is significantly intensified.A pack of STI was proposed with considering their peculiarities. This composition of STI was used in spacecrafts “Venus”, “Mars” and others.