For designing a small humanoid robot, aluminum is recommended due to its lightweight, cost-effectiveness, and strength, making it suitable for non-destructive applications. Wood is mentioned but may not be the best choice for a lightweight design. Casting resin is suggested for achieving humanoid shapes, while acrylic sheets are a viable option for other parts. The focus is on finding materials that balance lightness and economy without compromising structural integrity. Selecting the right materials is crucial for the overall performance and feasibility of the robot.