Hexamethylene diisocyanate (HDI) is the organic compound with the formula (CH2)6(NCO)2.

Aliphatic diisocyanates are used in specialty applications, such as enamel coatings which are resistant to abrasion and degradation by ultraviolet light.

These properties are particularly desirable in, for instance, the exterior paint applied to aircraft and vessels.

HDI is also sold oligomerized as the trimer or biuret which are used in automotive refinish coatings.

HDI is also used bisoxazolidine synthesis as the hydroxyl group on the molecule allows for further reaction with hexamethylene diisocyanate.