The present study is an attempt to investigate the effects of simultaneous pyrolysis activation processes and 3D network characteristic on structural, dielectric and electromagnetic interference (EMI) shielding properties of one-step activated carbon foam (CAs) filled in epoxy resin. Samples were synthesized via sol-gel process of resorcinol and formaldehyde followed by ambient pressure drying. To investigate the effect of pyrolysis process on structural properties and EMI shielding performance of samples, carbonization and activation processes were carried out simultaneously under CO2 atmosphere at varied residence time. To investigate the influence of 3D network characteristic on the dielectric and EMI shielding performance of the synthesized CAs, samples were ground down to two different particle sizes of 44 and 1 mu m. The former (samples with 44 gm in size) preserved carbons with network characteristic (CNC) and the latter turned into pulverized carbon (PCA) with no 3D network characteristic. The results revealed that the pyrolysis residence time had a meaningful effect on both structural and dielectric characteristics of the synthesized CAs. It was also shown that owing to the 3D network structure, the CNC samples provided several times higher shielding efficiency compared to their corresponding PCA. EMI shielding performance of CNC based composites containing 5 wt% exceeded 20 dB at a very thin thickness of 2 mm. Finally, it has been demonstrated that compared to the similar recent works, the prepared carbons exhibited a more efficient shielding performance at a lower loading fraction, indicating that these materials present advantages as microwave shielding. (C) 2018 Elsevier B.V. All rights reserved.