Reconstruction of 3D Conductive Networks in Metal‐Filled Elastomer Composites Indicates Dominance of Contact Resistances

Conductive polymer composites (CPCs) combine the stretchability of an elastomeric matrix with the electrical conductivity of a metallic filler. The 3D structure of this filler particle network (FPN) and the contact resistances between particles above percolation, key factors in the conductivity, are not well understood. Here, we introduce 3D reconstructions of FPNs of micron‐sized spherical silver particles in polydimethylsiloxane from focused ion beam scanning electron microscopy tomography. Analysis of the tomographic images provides the length and number of parallel conductive paths. The results show that the average contact resistance drops five orders of magnitude when increasing the silver loading from to , highlighting its dominating role for macroscopic conductivity rather than network structure. This links to 33% larger average area‐equivalent diameters of the contact spots. Diffusional tortuosity, a metric that quantifies flow restriction through narrow contact spots, proves that higher contact forces decrease current flow restrictions and thus, increase overall electrical conductivity. These conclusions are verified using a segregated CPC, and it is found that the addition of of insulating fillers at a constant silver loading of increases the conductivity 37‐fold and decreases the average contact resistance by two orders of magnitude.