A blend of enumerated nylon types is generally classified under 390810 if it falls within the described PA grades. However, if the blend's chemical character places it outside those enumerated types, 390890 may apply. A binding ruling from CBP is advisable for blends where the dominant polymer is ambiguous.

PA-6,6 has a higher melting point and better heat resistance, making it preferred for under-hood automotive parts, while PA-6 offers easier processing and lower cost, favoring textile and general-purpose applications. These differences drive distinct supply chains and can affect which grade a buyer specifies from a given country of origin.