Polyurethane sandals are primarily manufactured through injection molding, a process that requires significant initial investment, often exceeding $50,000 due to the cost of tooling. This method is favored for products like sandals because they are produced in large volumes, justifying the expense of hard tooling. While there are various techniques to form polyurethane products, injection molding is the most suitable for the specific shape and function of sandals. For detailed insights into the manufacturing process and raw materials used in making polyurethane sandals, resources like Wikipedia and specialized plastic molding websites can provide valuable information.