Abstract <p>Nonhardening sealants are used at refrigeration equipment manufacturing plants for temporary sealing of structures during assembly. The paper studies the properties of highly filled sealing compositions based on low-molecular polyisobutylene grade PB-1300 (with a polymer binder content of 10–15%) intended for temporary sealing of refrigeration equipment. It is shown that, in a certain concentration range, an increase in the filler content leads to an increase in strength. A necessary component of highly filled compositions based on a nonpolar oligomer and a polar filler is a compatibilizer, in this case, stearic acid. It is found that petrolatum can be used to regulate the properties of compositions under study, primarily their viscosity properties. However, it should be taken into account that its introduction leads to deterioration of the physical and mechanical properties of compositions. These studies are of scientific and practical interest to developers and manufacturers of nonhardening highly filled sealing materials.</p>