When evaluating cotton jersey, the most critical factor is the GSM (Grams per Square Meter), which determines the fabric's weight and thickness; typically, 140-160 GSM is used for lightweight t-shirts, while 200+ GSM is preferred for premium, heavy-duty apparel. You must also verify the yarn count (e.g., 30s, 40s)—higher numbers indicate finer, softer yarns. Additionally, check the composition percentage, specifically if it is 100% Combed Cotton for maximum softness or a Cotton-Spandex blend (usually 5%) to ensure better shape retention and elasticity.