One dimensional quantum-dot superlattices (1D-QDSLs) consisting of acoustically mismatched materials are demonstrated theoretically to possess sub-1 W m^-1 K^-1 thermal conductivity in the 50-400 K range of temperatures. We consider coherent Si/Ge 1D-QDSLs, as well as model Si/plastic, Si/SiO₂ and Si/SiC 1D-QDSLs. The phonon energy spectra and group velocities are obtained in the framework of the face-centered cubic cell model of lattice dynamics. On this basis, lattice thermal conductivity is calculated. A strong reduction of lattice thermal conductivity in 1D-QDSL structures in comparison with homogeneous rectangular Si nanowires is explained by the exclusion of phonon modes folded in superlattice segments from the heat flow and by the decelerating action of Ge, SiO₂, or plastic materials. Thus, the 1D-QDSL structures act as effective phonon filters, eliminating a significant number of phonon modes from thermal transport. The obtained results imply a perspective of quantum-dot superlattices as thermoelectric materials and thermal insulators.