Continuous powering of wearable electronics and personalized biomonitoring systems remains a great challenge. One promising solution is the use of thermoelectric generators (TEGs) that convert body heat to electricity. These energy harvesters must conform to curved surfaces and minimize thermal barriers to maintain efficiency while still exhibiting durability under large deformations. Here, highly efficient, stretchable thermoelectric generators made of inorganic semiconductors and printed multifunctional soft matter are introduced. Liquid metal elastomer composites with tailored microstructures are printed as highly conductive thermal interface materials and stretchable interconnects. Additionally, elastomer composites with hollow microspheres are formulated to print a deformable and lightweight thermal insulator within the device. These stretchable thermoelectric wearables show an excellent performance by generating an open‐circuit voltage of 392 mV and a power density of ≈650 µW cm−2 at ∆T = 60 °C and withstanding more than 15 000 stretching cycles at 30% strain. Furthermore, the additive manufacturing process is leveraged by direct writing of the TEGs on textiles to demonstrate their seamless integration and by 3D printing of stretchable heatsinks to maintain a large temperature gradient across the device and to study the effect of convective heat transfer on device performance.

Electrostatic patterning has improved the performance of devices incorporating electrospun fibers in a wide variety of applications. However, the impact of process parameters on the final fiber pattern in these systems is rarely analyzed. Herein, a systematic analytical approach is developed to define quantitative metrics related to fiber patterning. Three‐dimensional patterned dielectric elastomer collectors are fabricated via solution‐casting polydimethylsiloxane with embedded carbon black or liquid metal droplets. Fiber patterning metrics are used to evaluate the effect of collector parameters such as insulating layer thickness, electrical ground surface area, and three‐dimensional pattern geometry. Dielectric layer parameters such as conductive material concentration and particle diameter are also investigated. Using this framework, the best‐performing collector is shown to improve selectivity 30‐fold, uniformity ninefold, reproducibility eightfold, and increase fiber volume by one order of magnitude. Furthermore, eutectic gallium indium liquid metal and scaled‐up pattern geometries demonstrate the tunability of this approach and broad applicability of systematic fiber pattern analysis. This rational approach to patterned fiber development can be applied to virtually any method or pattern to better understand the fiber patterning processes.