When sourcing tie-dye shirts, prioritize fabric composition, typically 100% combed cotton or high-grade cotton-polyester blends (60/40), to ensure optimal dye absorption and skin breathability. Pay close attention to the fabric weight, usually measured in GSM (Grams per Square Meter); a range of 160-200 GSM is ideal for standard retail quality. Additionally, verify the colorfastness rating, which should be Grade 4 or higher to prevent bleeding during washing, and ensure the use of reactive dyes which provide more vibrant and permanent results compared to pigment dyes.