How does HDI differ from aromatic isocyanates like TDI and MDI in downstream use?

How does HDI differ from aromatic isocyanates like TDI and MDI in downstream use?
HDI belongs to the aliphatic diisocyanate family, distinguished by its linear saturated carbon chain without benzene rings. This structure gives HDI-based polyurethanes superior non-yellowing, color and gloss retention, anti-chalking, oil resistance, and weatherability compared to aromatic isocyanates such as TDI and MDI, which tend to oxidize and yellow. As a result, HDI is the preferred raw material for high-end applications including automotive refinish paints, original equipment coatings, wood coatings, and adhesives. While TDI and MDI dominate overall isocyanate consumption due to lower cost and larger volumes, HDI commands a premium niche where durability and appearance are critical. Its production relies on hexamethylenediamine feedstock, whose price fluctuations directly impact HDI economics.