  Designing materials with low thermal conductivity (\k{appa}) is of demand for
thermal protection, heat insulation, thermoelectricity, etc. In this paper,
based on the start-of-art first-principles calculations, we propose a framework
of a 1T-sandwich structure for designing materials with low \k{appa}. The
1T-sandwich structure is the same as the well-known transition metal
dichalcogenide (TMD) but with light Carbon atoms in the middle plane. Using
different atoms to fill the outer positions, a few novel two-dimensional
materials are constructed as study cases, i.e., Mg2C, Janus MgBeC, Be2C, and
Mo2C. With a systematic and comparative study, the \k{appa} are calculated to
be 3.74, 8.26, 14.80, 5.13 W/mK, respectively. The consistent values indicate
the stable behavior of low \k{appa} in the 1T-sandwich structure, being
insensitive to the component. Our study would help design advanced functional
materials with reliable heat transfer performance for practical applications,
which reduces the influence of unavoidable impurities.
