When sourcing wholesale T-shirts, the fabric weight is measured in GSM (Grams per Square Meter); standard T-shirts range from 160-180 GSM, while premium 'heavyweight' options exceed 200-240 GSM. You must verify the fiber content, such as 100% Combed Cotton for softness, Organic Cotton for sustainability, or Polyester-Cotton blends (TC/CVC) for better shape retention and wrinkle resistance. Always request a fabric swatch or pre-production sample to test for hand-feel, pilling resistance, and transparency.