The densification behaviour of mixtures of soft and hard powders during pressing is investigated. Several experimental studies using materials with miscellaneous mechanical and morphological features are summarised. The influence of mixture characteristics on the densification kinetics is discussed and several mechanisms explaining the influence of hard particles on the densification behaviour are proposed. Two main cases are distinguished. When the applied pressure is low, with regard to the yield stress of soft particles, the densification is mainly due to particle rearrangement and is favoured by a high fraction of hard particles. When soft particle deformation is the main densification mechanism, hard particles hinder the densification, with more or less significance depending on whether they are mostly isolated, are grouped in aggregates or form a percolating network.