Wearable heaters that can retain conformal contact with human skin have attracted significant attention in recent years due to their enormous potential in thermotherapy. Existing strategies for wearable heaters are constrained by fixed configurations or dimensions, which limit their broad utilities in bio-integrated applications requiring heaters of various sizes. Here, we report a mechanics-guided design of wearable network heaters based on the lattice structure with the negative Poisson’s ratio combined with the uniaxial stretch, which allows for the easy realization of heaters with different sizes and relatively uniform heating performance. Theoretical and computational mechanics studies reveal the fundamental aspects of the design and operation of the network heaters. Thermal analyses of the network heaters integrated with human skin are performed to investigate the influences of design parameters on the skin temperature. This study offers an easy route for wearable network heaters and provides design guidelines for their fabrications.