Hexamethylene diisocyanate (HDI) is a chemical compound commonly used in the production of polyurethane materials. It is a colorless liquid with a strong odor and is primarily utilized in coatings, adhesives, and sealants due to its ability to form durable and flexible products. HDI is classified as an isocyanate, which means it contains two isocyanate functional groups. This structure allows it to react with polyols to create polyurethanes. However, exposure to HDI can pose health risks, including respiratory issues and skin irritation, making proper handling and safety precautions essential in industrial settings.