The thermal shroud of a thermal vacuum chamber is in most cases not perfectly closed. There are holes for windows and feedthroughs and some stands inside the shroud which influence the thermal behavior of the test article. Size and thermo- optical properties of the covers of the holes determine the effect on the temperature change of the test article. This influence is investigated for different cases as they occur in a thermal test chamber. Covers made of aluminized or black KAPTON and painted metal sheets are investigated.Mechanical fixtures are needed for installation of the test articles. By constraints of the test setup these fixtures often can't be designed as adiabatic or actively temperature controlled. For the case of large test articles with relatively low thermal heat capacity as reflectors for telecommunication satellites, the influence of the fixture on the final temperature is discussed for different cases and an optimized solution is presented. These consideration are of interest especially for the cold case, when temperatures as close as possible to the liquid nitrogen temperature are required for the temperature of the test article.