3920.51 - Of poly(methyl methacrylate):

This HTS category, 3920.51, specifically covers plates, sheets, film, foil, and strip made from poly(methyl methacrylate) (PMMA), also commonly known as acrylic. These materials are characterized by their noncellular structure and the absence of reinforcement, lamination, support, or combination with other materials. This means the products are solid forms of acrylic plastic without internal air bubbles or structural additions.

The distinction from its sibling category, 3920.59, lies in the specific polymer composition. While both fall under "Other plates, sheets, film, foil and strip, of plastics, noncellular and not reinforced, laminated, supported or similarly combined with other materials," this sub-heading is exclusively for those made of poly(methyl methacrylate). Sibling categories like 3920.59 would encompass similar plastic forms but made from different acrylic polymers or copolymers.

Within this poly(methyl methacrylate) classification, further subdivisions exist to refine classification. The subcategories, 3920.51.10 (Flexible) and 3920.51.50 (Other), differentiate based on the physical flexibility or rigidity of the acrylic sheet, film, or strip. This allows for more precise identification and duty assessment based on the intended use and physical properties of the exported or imported acrylic product.