Cotton and polyester are the two most common t-shirt fabrics, and each brings something different to the table. Cotton is soft, breathable, and gets better with age, making it the go-to choice for everyday comfort. It absorbs moisture well, which is great for warm weather, though it can wrinkle more easily and take slightly longer to dry.
Polyester is more durable, resists wrinkles, and dries quickly, but it doesn't breathe as well as cotton and can feel less comfortable against the skin over a full day of wear. Many brands now blend the two — a cotton-polyester mix gives you the softness of cotton with the shape retention and durability of polyester. If comfort is your priority, go for 100% cotton; if you want something low-maintenance for travel or workouts, a blend or polyester tee is the better call.