The influence of the initial configuration of glass mat and polypropylene on the deconsolidation during post-processing of the resulting composite is investigated. Deconsolidation experiments of a classic type of glass mat reinforced thermoplastic (GMT) produced by infiltration and a new type of commingled mat produced by consolidation are carried out, followed by void content measurements. A model predicting the kinetics of deconsolidation and final void content after reheating is applied to the two different systems. The numerical results completed by compressive tests carried out on both initial dry glass preforms show that the difference in fibre bundle arrangements leads to different deconsolidation kinetics and final state.