Aromatic types contain benzene ring structures and exhibit high reactivity, providing strong adhesion and heat resistance while achieving high hardness and strength.
Typical examples include TDI and MDI, which are used in polyurethane foams, adhesives, and industrial coatings.

Aliphatic types feature linear or cyclic carbon chain structures with excellent UV stability, resulting in minimal discoloration after curing.
Typical examples include HDI and IPDI, used in electronic and electrical protective materials and composite binders.