The European Commission defines a nanomaterial as “a natural, incidental or manufactured material containing particles, in an unbound state or as an aggregate or as an agglomerate and where, for 50 % or more of the particles in the number size distribution, one or more external dimensions is in the size range 1 nm - 100 nm.”
Nanomaterials are divided into three groups according to their structure:
Nanoparticles and fullerenes
Nanotubes and nanofibers