9404.29 - Of other materials:

This HTS category, 9404.29, encompasses mattresses that are constructed from materials other than cellular rubber or plastics, and are not specifically covered by the sibling category 9404.21. These mattresses are characterized by their filling or internal structure, which can include a wide array of materials such as natural fibers (e.g., cotton, wool, down), synthetic fibers, or composite materials, whether or not they are encased in a fabric cover. The fundamental aspect of this classification is the material composition of the mattress core or stuffing.

This category is distinct from 9404.21, which specifically covers mattresses made from cellular rubber or plastics. Therefore, if a mattress's primary internal material is foam rubber, latex, or any other cellular polymeric substance, it would fall under 9404.21. Conversely, mattresses filled with cotton batting, synthetic polyester fiberfill, or even innerspring units with traditional padding would be classified under 9404.29, provided they do not meet the criteria for cellular rubber or plastic construction.

Within 9404.29, further subclassification is made based on the specific material of the mattress. The subcategory 9404.29.10 is designated for mattresses made of cotton. All other mattresses not falling into the cotton subcategory, but still meeting the general criteria of 9404.29 (i.e., not cellular rubber or plastic), are classified under the residual category 9404.29.90. This allows for a more granular breakdown of mattress types based on their primary constituent materials.