When evaluating spandex denim, you must focus on the Composition Ratio, typically ranging from 95% cotton / 5% spandex to 98% cotton / 2% spandex. The Weight (GSM/Ounces) is critical; lightweight denim (under 12oz) is ideal for summer wear, while heavyweight (above 12oz) is for premium durable jeans. Additionally, verify the Elasticity Recovery Rate to ensure the fabric does not 'bag out' after stretching, and check the Yarn Count (e.g., 10s, 12s, 16s) which determines the fabric's texture and strength.