Phenol–formaldehyde (phenolic) thermosets are known for excellent heat and chemical resistance, high flame retardance, and good mechanical performance. However, phenolics are also known for their high brittleness, and tendency to form voids, due to a condensation reaction forming water during curing. These voids can decrease the mechanical performance of the resultant phenolic composite and introduce undesirable performance characteristics. This work aims to develop a technique that uses high-pressure infiltration to obtain dense phenolic matrix composites, with commercially available resin and fiber reinforcement. The high-pressure system developed in this work is compared to a conventional low-pressure resin infusion technique, and the porosity after each infusion is analyzed. A model of the low- and high-pressure systems was developed, and the predicted time of infiltration was compared to the experimental results. The high-pressure system had 97% less open porosity after infusion than the low-pressure technique, suggesting that it can produce a higher-quality and better-performing phenolic composite than conventional techniques. Also, the mechanical test performed indicates improved performance for the high-pressure injection with a 30.73% increase in ultimate tensile strength in comparison to low pressure, indicating better mechanical performance. © 2024 Society of Industrial Chemistry.