Ultra-high molecular weight polyethylene (UHMW-PE) is an extremely long-chain polymer produced as fibers using a gel-spinning process. These fibers have a high degree of molecular orientation and crystallinity compared to bulk polyethylene, leading to exceptional mechanical and thermal properties. Commercial fabrics containing UHMW-PE are currently used in personal armor, motorcycle and climbing gear, and high-performance sports equipment owing to their high strength, durability, and abrasion-resistance. In addition to superior mechanical properties, the UHMW-PE fibers exhibit very high axial thermal conductivity. Recent studies in the literature have focused on characterizing the thermal properties of these individual fibers. However, to assess its ability to serve applications in thermal management of flexible electronic devices requires an understanding of the thermal behavior of UHMW-PE in the fabric form that will ultimately be used to construct flexible heat spreading materials. This work presents the thermal characterization of composite UHMW-PE fabrics using an infrared microscopy-based approach. The infrared temperature measurements are performed in a vacuum environment using a nichrome heater wire contacting the fabric sample in a suspended arrangement. The steady-state temperature profiles of the wire and the fabric sample are analyzed to deduce the thermal conductivity of the fabric. Using this method, the thermal conductivities of composite fabrics consisting of varying volume fractions of UHMW-PE are measured and compared with other conventional flexible materials/fabrics. The results indicate that the composite UHMW-PE fabrics have lower thermal conductivities compared to individual UHMW-PE fibers, but significantly higher thermal conductivities than the conventional materials, thereby showcasing their promise as flexible and wearable heat spreaders. Relevant Track: Internet of Things (Flexible Substrates, Thermal and Mechanical Properties)