When evaluating cotton elastic fabric, you must focus on the composition ratio, typically a blend of 95% cotton and 5% spandex (elastane) for standard stretch, or higher spandex content for athletic wear. Pay close attention to the fabric weight (GSM - Grams per Square Meter); for T-shirts, 160-200 GSM is standard, while leggings require 250-300 GSM to ensure non-transparency. Additionally, verify the yarn count (e.g., 32s, 40s), as higher numbers indicate a finer, smoother, and more durable thread.