GSM (grams per square meter) is the number that tells you how heavy a tee's fabric is. In Georgia, where the humidity can make you second-guess every layer, a 180 GSM Windbar tee is your best bet—it's structured enough to look sharp but breathable enough for a July afternoon. Check the product page for the GSM, or if you're in a store, feel the fabric: it should feel substantial, not flimsy.