When evaluating ribbed cotton, the most critical factor is the GSM (Grams per Square Meter), which determines the fabric's weight and opacity; for standard apparel, 180-250 GSM is typical. You must also verify the rib structure (e.g., 1x1, 2x2, or 4x4) to ensure it meets your design's elasticity and aesthetic requirements. Additionally, check the fiber composition—while 100% cotton offers breathability, a blend with 5-10% Spandex/Elastane is often necessary for superior shape retention and recovery.