The cotton content percentage is the dividing line: if the fabric contains 85% or more cotton by weight, it belongs in 5209 (specifically the denim subheading 520942). If cotton is below 85% and the remaining fiber is mainly manmade, the fabric moves to 5211 (specifically 521142 for the denim construction). Fiber-content testing is essential before making this determination.

No. Heading 5211 requires that the non-cotton content consist mainly or solely of manmade fibers. A fabric where wool or another natural fiber is the predominant non-cotton component would instead fall under heading 5212, which covers cotton blends mixed with fibers other than MMF.