This paper aims to show the relationship between various scales of porosities and densities in plant particles packing (hemp shiv) used for building applications, and the understanding of the absorption, mechanical, thermal and acoustical behaviours of particles used as loose aggregates or in bio-based concretes. Theoretical models using the different porosity and density scales of hemp shiv packing are assessed, and compared with experimental results. It is shown that particle open porosity and swelling drive the water absorption capacity. Strong correlations can be found between compression behaviour of the particle stacks and the three scales of density: bulk, particle and skeleton. In the same way, the acoustics is affected by both inter-particle and part of intra-particle porosities. This communication is linked with another contribution (Part 1), dealing with multiscale measurements of porosities and densities of such bio-based aggregates.