3506.91 - Adhesives based on polymers of headings 3901 to 3913 or on rubber:

This category, HTS 3506.91, encompasses adhesives that are not specifically classified elsewhere. It primarily covers adhesives formulated from polymers falling within headings 3901 to 3913 or from rubber. The key characteristic is that these adhesives are "prepared," meaning they are ready for use or have undergone some form of processing beyond the raw polymer or rubber. This includes glues and other adhesives not specifically mentioned in other subheadings of 3506, as well as products designed for use as adhesives and presented in retail packaging with a net weight not exceeding 1 kg.

Within the "Other" category at this level (3506.91), there is a distinction based on specific applications and general groupings. The sibling category, 3506.99.00.00, covers adhesives not falling under 3506.91, implying that 3506.91 is reserved for a more specific set of prepared adhesives based on polymers or rubber.

To further refine classification, HTS 3506.91 is divided into subcategories. HTS 3506.91.10.00 specifically addresses optically clear free-film adhesives and optically clear curable liquid adhesives. These are distinguished by their optical properties and their intended use solely or principally in the manufacturing of flat panel displays or touch-sensitive screen panels. The remaining products within this broader category are then classified under HTS 3506.91.50.00, labeled as "Other," which captures all other prepared adhesives based on polymers or rubber not meeting the specific criteria of the optically clear adhesive subheading.