In this article the role of voids or particulate inclusions of different sizes on mechanical properties and particularly on toughness in several polymers is discussed. With decreasing void sizes and intervoid distances, the influence of the interphase material around the voids becomes more important and characteristic changes in the nano- and micro-deformation mechanisms appear. These mechanisms are revealed by several techniques of electron microscopy within rubber modified polymers, nanocomposites and nanofibres respectively. Three nanoscopic toughness enhancing mechanisms are described in detail: thin layer yielding, nanovoid-modulated craze-formation, and the core flattening mechanism. The action of these mechanisms constitutes a distinct advantage of nanovoids over microvoids. (c) 2013 Elsevier Ltd. All rights reserved.