When evaluating denim quality, focus on fabric weight (measured in ounces); lightweight denim (8-10 oz) is suitable for summer, while mid-to-heavyweight (12-14 oz) offers better durability. Check the composition ratio, specifically the percentage of Spandex or Elastane (usually 1-3%) for stretch comfort versus 100% cotton for authentic vintage styles. Additionally, inspect the stitch density (SPI - stitches per inch), ensuring a minimum of 8-10 stitches per inch to prevent seam failure under tension.