The electrical conductivity of carbon‐black‐filled composites depends on the structure of the carbon black, the morphology of the polymer, and the processing history of the composite. For identical processing conditions highly porous carbon blacks produce more conductive composites at lower filler loadings than structured blacks. Moreover, porous carbon black composites are less sensitive to processing history than structural blacks. The greater the degree of internal phase segregation produced during polymer solidification, the lower the resistivity of the resulting composite. Electrically conductive carbon‐black‐filled composites can be produced with resistivities low enough to provide 30 dB of electromagnetic interference shielding attenuation. The shielding attenuation‐volume‐resistivity relationship appears to follow predictions based on plane wave analysis when the samples are tested under plane wave radiation conditions.