Flexible polyurethane foam manufacturers are the primary consumers, particularly those supplying furniture, mattress, and automotive seating markets where flammability standards require integrated flame-retardant treatment. The reactive nature of these phosphonates — bonding into the polymer rather than migrating out — makes them preferred over additive alternatives in applications with durability or emissions requirements.

The key is the specific chemical identity of the principal constituents: heading 382491 requires that the mixture be mainly composed of the named dioxaphosphinane-methyl methylphosphonate and its bis counterpart. Mixtures where other phosphate esters (e.g., TCPP, TDCPP) predominate would fall outside this heading, typically under 382499 or other Chapter 38 subheadings depending on composition.