When evaluating denim quality, focus on fabric weight, measured in ounces (oz). Lightweight denim (under 12 oz) is suitable for summer or stretch styles, while heavyweight denim (14 oz and above) offers superior durability and a premium feel. Additionally, check the composition: 100% cotton provides an authentic vintage feel, while 2-3% Spandex/Elastane is essential for slim-fit or comfort-oriented styles. Ensure the use of reinforced stitching (chain stitching) at high-stress points like the crotch and pockets to prevent tearing.