@officiallytracytime: Here is the scoop on picking the perfect size for your Mellow cooling pajamas sets. You pick your fit, regular or oversized in addition to your set size of S, M, L & XL. In my opinion they are so stretchy that even me as a usual XL size could easily fit a medium comfortably. Perfect for travel as they are lightweight, take up very little space and are great for hot climates or ladies over 50 dealing with flashes.