Heading 6004 applies to knitted or crocheted fabrics wider than 30 cm that contain more than 5% by weight of elastomeric yarn (such as spandex/Lycra), provided they are not pile fabrics. Fabrics with 5% or less elastomeric content that do not otherwise qualify for 6001 or 6003 fall into the residual headings 6002 or 6006. The elastomeric yarn percentage by weight — not by visual stretch or hand feel — is the controlling criterion.

Warp-knit fabrics (6005) are produced on a warp-knitting machine where yarns run lengthwise and are looped together simultaneously across the fabric width, creating a stable, run-resistant structure used in lingerie, sportswear linings, and technical applications. Weft-knit fabrics — where a single yarn runs across the width — fall under 6001, 6002, 6003, 6004, or 6006 depending on their specific characteristics. Machine type and loop direction are the technical distinguishing factors.