Thermal switching is an advanced smart thermal control technology in thermal management systems, such as refrigeration, thermal resistors, and space technology. Controlling lattice thermal conductivity (${\kappa }_{\mathrm{l}}$) through structural phase transitions provides an effective strategy for thermal switching applications. Here, we investigate the dual-channel thermal transport in polar and antipolar phases of NaZnSb using first-principles calculations. Compared with the polar phase, the antipolar phase exhibits a markedly lower ${\kappa }_{\mathrm{l}}$, leading to thermal switching ratios of 2.51, 2.06, and 1.75 at 300, 500, and 700 K, respectively. Such large ratio is mainly induced by the particlelike thermal conductivity (${\kappa }_{\mathrm{p}}$). Spectral and cumulative ${\kappa }_{\mathrm{p}}$ analyses reveal that heat transport in both phases is dominated by acoustic and low-frequency optical phonons with mean free paths of 2–20 nm. The reduced ${\kappa }_{\mathrm{p}}$ in the antipolar phase originates from stronger LA-optical phonon mixing, lower phonon group velocities, higher scattering rates, larger phase space, and enhanced anharmonicity. The projected crystal orbital Hamilton population analyses further show stronger Zn-Sb and Sb-Sb antibonding interactions in the antipolar phase, which weaken bonding, enhance atomic vibrations, and suppress sound velocity. This work elucidates the microscopic origins of reduced thermal conductivity across the polar to antipolar transition, providing valuable guidance for designing ferroelectric/antiferroelectric thermal switching materials.

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• Antiferroelectricity
• Ferroelectricity
• Thermal conductivity
• 3-dimensional systems
• First-principles calculations