Bulk materials (>100 nm in size) are expected to have constant physical properties (such as thermal and electrical conductivity, stiffness, density, and viscosity) regardless of their size, for nanoparticles, however, this is different: the volume of the surface layer (a few atomic diameters-wide) becomes a significant fraction of the particle's volume; whereas that fraction is insignificant for particles with a diameter of one micrometer or more. In other words, the surface area/volume ratio impacts certain properties of the nanoparticles more prominently than in bulk particles.