The effect of particle contact-contact interaction and pore geometry is studied for the pressure-density relationship of powders undergoing hydrostatic compaction. The study is restricted to a two-dimensional array of cylindrical particles. Slip-line field theory is used to analyse the rigid-perfectly plastic response and the finite element method is used to explore the effect of material strain hardening. For both. material descriptions, contact-contact interaction has a strong influence on the compaction process beyond the initial stage. The theoretical predictions are compared with experimental results for hydrostatic compaction of plasticene cylinders.