Background <p>Heat-polymerized acrylic resin is one of the most widely used polymeric materials in denture fabrication. Therefore, improving these resin materials is crucial to ensuring optimal denture properties and performance.</p> Purpose <p>This in vitro study aimed to evaluate the influence of polyurethane incorporation on the mechanical properties of heat-polymerized PMMA denture base resin.</p> Materials and methods <p>Polymethyl methacrylate (PMMA) is used to produce dentures due to its aesthetics and ease of manufacture. However, it has low impact and flexural strength. Tough and flexible polyurethane was employed to overcome these difficulties. A control group with unmodified PMMA (30 samples) and an experimental group (90 samples) with 1%, 3%, and 5% polyurethane received 120 heat-polymerized acrylic resin samples (10 samples per test). Experimental samples were compared to the control group for flexural strength, impact strength, and hardness to see how polyurethane addition influenced resin mechanical properties.</p> Results <p>Based on composition, polyurethane polymers boosted PMMA’s flexural, impact, and surface hardness. Control samples were unmodified PMMA and 1%, 3%, and 5% polyurethane volume fractions. Statistical analysis used one-way ANOVA and Tukey’s post-hoc test to assess group differences, with a significance threshold of p &lt; 0.05.</p> Conclusions <p>The interpenetrating polymer network composite significantly influences and improves the mechanical properties of the heat-polymerized denture base resin, making it more challenging, stronger, and resistant to flexural and hardness stresses.</p>