Navid Kazem (left), Jonathan Malen (center), and Carmel Majidi (right) demonstrate the elasticity of a strip of "thubber." (Credit: Carnegie Mellon University)

A thermally conductive rubber material represents a breakthrough for creating soft, stretchable machines and electronics. The new material, nicknamed “thubber,” is an electrically insulating composite that exhibits an unprecedented combination of metal-like thermal conductivity and elasticity similar to soft, biological tissue that can stretch over six times its initial length.

The combination of high thermal conductivity and elasticity is especially critical for rapid heat dissipation in applications such as wearable computing and soft robotics, which require mechanical compliance and stretchable functionality. Applications could extend to heated garments for injury therapy.

The key ingredient in thubber is a suspension of non-toxic, liquid metal microdroplets. The liquid state allows the metal to deform with the surrounding rubber at room temperature. When the rubber is prestretched, the droplets form elongated pathways that are efficient for heat travel. Despite the amount of metal, the material is also electrically insulating.