Hexamethylene diisocyanate (HDI) is a clear to pale yellow liquid characterized by a slightly pungent odor. It exhibits low water solubility and reacts slowly in aqueous environments. At room temperature, its relative density is approximately 1.05. Its key phase transition temperatures include a boiling range of 255–261°C and a freezing or melting point ranging from -67 to -55°C. According to vapor pressure data, the saturated concentration of HDI is 46 mg/m³ at 20°C and 137 mg/m³ at 30°C.

As an aliphatic polyisocyanate, HDI is primarily used in the manufacture of polyurethane products with good resistance to yellowing. Compared with aromatic diisocyanates, it exhibits lower reactivity. The absence of aromatic rings in HDI contributes to polyurethane elastomers with moderate hardness and strength, as well as good flexibility. HDI is flammable and insoluble in cold water, but it dissolves in organic solvents such as benzene, toluene, and chlorobenzene. Its physical properties include a melting point of -67°C, a relative density of 1.04, a boiling point of 130–132°C at 99,725 Pa, a flash point of 140°C, and a refractive index of 1.4530. HDI reacts with alcohols, acids, and amines, while contact with water or bases causes decomposition. In the presence of metal chlorides, including copper or iron chlorides, it can also undergo polymerization.

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HDI is the most significant monomer among aliphatic diisocyanates (ADI), representing approximately 60% of total ADI demand. The majority of HDI is converted into HDI biuret or HDI trimer. HDI and its biuret and trimer derivatives are important raw materials for manufacturing polyurethane coatings and polyurethane elastomers.

Polyurethane coatings based on HDI, HDI biuret, or HDI trimer offer excellent weather resistance and resistance to yellowing. As a result, they are widely used in various industries, including aerospace, automotive, construction, wood finishing, plastics, and leather processing. In addition, these derivatives are used as crosslinking agents for drying alkyd resins and as raw materials for synthetic fibers. They are also applied in the production of aliphatic polyurethane coatings and serve as leather finishing agents.