When sourcing blank T-shirts, the fabric weight (GSM - Grams per Square Meter) is the primary indicator of quality; standard shirts range from 150-180 GSM, while heavy-duty premium options exceed 200+ GSM. You must verify the material blend, such as 100% Combed Cotton for softness, Organic Cotton (GOTS certified) for sustainability, or CVC (Chief Value Cotton) blends for better shrinkage resistance and durability. Always request a fabric swatch or pre-production sample to test for hand-feel and breathability.