Introduction. The metal–composite technology (MCT) for manufacturing tool bodies using an “SLM shell + metal–polymer composite material (Metal–polymer/MPCM)” enables the implementation of curvilinear coolant/lubricant supply channels and reduces the additively manufactured metal volume; however, the quality of filling thin-walled cavities is critically determined by the level of gas porosity of the filler. Gas porosity degrades the thermal conductivity and load-bearing capacity of the MPCM, reduces the stability of filling in critical zones near the SLM shell wall and adjacent to the channels, and increases properties dispersion and the risk of defects during tool operation. The purpose of the work is to experimentally establish the relationship between MPCM gas porosity and residual pressure under vibro-vacuum degassing and to justify a technologically preferable vacuum range for application in MCT tool bodies. Methodology. The study was carried out using a vibro-vacuum setup comprising a preliminary degassing chamber and a casting chamber with low-frequency vibration. Standard MPCM samples were produced for each vacuum condition. Porosity was evaluated using an adopted scoring scale based on microscopy (analysis of pore distribution, clustering, and characteristic defect sizes). Results and discussion. The experiment revealed a stable nonlinear (V-shaped) trend: as pressure decreases from atmospheric to approximately 450 Pa, the average porosity score monotonically decreases and reaches a minimum in the 400–350 Pa range (1–2 points). Further vacuum intensification below 300 Pa leads to vigorous gas evolution and foaming (“boiling”), accompanied by a sharp increase in defectiveness (up to 3–5 points). Conclusions. The identified optimal vacuum range of 400–350 Pa is recommended as a compromise between effective removal of entrapped gas and avoidance of the foaming, ensuring reproducible filling quality of MPCM within SLM shells in MCT tool-bodies manufacturing.