Because the fabric exceeds 170 g/m², it falls in heading 5514 rather than 5513. Within 5514, a dyed polyester-cotton twill with under 85% polyester is classified under subheading 551422. Confirming both the weight per square meter and the weave construction is essential before selecting the tariff line.

The 'mixed mainly with cotton' condition requires that cotton be the predominant secondary fiber by weight. A small elastane addition does not disqualify the fabric from this heading as long as cotton remains the dominant non-synthetic component. If another fiber (such as wool or a manmade filament) exceeds the cotton content, the fabric may shift to heading 5515 or another heading.