Highly Stretchable Polymer Composite with Strain‐Enhanced Electromagnetic Interference Shielding Effectiveness

Polymer composites with electrically conductive fillers have been developed as mechanically flexible, easily processable electromagnetic interference (EMI) shielding materials. Although there are a few elastomeric composites with nanostructured silvers and carbon nanotubes showing moderate stretchability, their EMI shielding effectiveness (SE) deteriorates consistently with stretching. Here, a highly stretchable polymer composite embedded with a three‐dimensional (3D) liquid‐metal (LM) network exhibiting substantial increases of EMI SE when stretched is reported, which matches the EMI SE of metallic plates over an exceptionally broad frequency range of 2.65–40 GHz. The electrical conductivities achieved in the 3D LM composite are among the state‐of‐the‐art in stretchable conductors under large mechanical deformations. With skin‐like elastic compliance and toughness, the material provides a route to meet the demands for emerging soft and human‐friendly electronics. A highly stretchable polymer composite with three‐dimensional liquid metals exhibits strain‐enhanced electromagnetic interference shielding efficiency over a wide range of frequencies. With an unprecedented combination of metal‐like electromagnetic shielding capability, unusual strain‐enhanced electrical conductivity, outstanding stretchability, and skin‐compatible mechanical properties, this material fills an important gap with regard to stretchable materials that are indispensable to soft electronics.