The outer sole is the component that contacts the ground in normal use. When multiple materials are present, the outer sole is identified by the material making up the greatest surface area in contact with the ground. CBP and the HS Explanatory Notes provide detailed guidance, and laboratory analysis of cross-sections is sometimes required for composite constructions.

Athletic shoes with a rubber or plastic outer sole and a textile upper classify under heading 6404, not 6402. Heading 6402 requires both the outer sole AND the upper to be of rubber or plastics. When the upper is textile — even if the sole is rubber — the correct heading is 6404.

Yes. Heading 6406 covers parts of footwear including removable insoles, heel cushions, outer soles and uppers sold separately, and gaiters. However, textile insoles that are more akin to textile articles may be reviewed under chapter 63, and the distinction can require a binding ruling for novel constructions.