When sourcing cotton shirts, the yarn count (e.g., 40s, 60s, 80s) is a primary indicator of quality; higher counts signify a finer, smoother fabric. You should prioritize Long-Staple Cotton (LSC) or Egyptian Cotton for premium lines due to their superior durability and softness. Additionally, verify the fabric weight (GSM) to ensure it matches the intended season—typically 110-150 GSM for standard dress shirts. Ensure the supplier provides colorfastness test reports (Grade 4 or higher) to prevent fading after multiple washes.