After long storage, a well-known problem related to missing the flexibility of the plastic explosives usually appeared. In this work, the reformulation of old PETN plastic explosives is presented. The plastic explosive was modified by adding a polymeric matrix based on a non-energetic thermoplastic binder plasticized by dibutyl phthalate (DBP). The crystal morphology after modification was studied by scanning electron microscope (SEM). The heat of combustion was determined experimentally. The compatibility of PETN plastic explosive with the polymeric matrix was studied by vacuum stability test. Sensitivity to impact and friction were determined. The detonation velocity was measured experimentally It was concluded that the old explosive is compatible with the polymeric matrix, and the sensitivity is close to that of the traditional plastic explosives. The detonation velocity is slightly lower than Semtex 1A.