Cotton retains moisture when wet. When you sweat it will become saturated and lose most of its breathability. This will make the shirt uncomfortable and heavy. Furthermore, if the surrounding temperature cools the shirt will take a long time to dry and you will start to feel cold from the dampness. Cotton is the worst performing fabric for high perspiration sports.
Synthetic clothes are ideal for high perspiration activities.
Stick to synthetics for high intensity sports that produce high volumes of sweat. There are no fabric that can wick and evaporate the high levels of preparation cause by intense sports. Therefore, the goal is to use fabrics that will not absorb moisture. Contrary to popular belief, synthetics do not wick (capillary action) moisture well. Rather, synthetics transfer small amounts of moisture over the surface of fibers and avoid absorption within.
Running clothes tend to be made of synthetic fabrics that are loosely woven. This loose weave provides gaps for air flow and little surface area for moisture to adhere to. Synthetic fibers will become quickly saturated with and low volume of moisture and then the excess moistures flows off the body.
Quick to dry.
Due to the minimal surface area of the loosely woven synthetic fabrics, a typical wet running shirt is only holding a small amount of moisture, and all of that is on the surface of the fibers. Therefore, the moisture will evaporate quickly once the perspiration stops or the shirt is hung up.
Poor Odor resistance.
Since synthetics tend to absorb bacteria so they will develop odor quickly. Most synthetic running clothing will need to be washed often. Odor resistant treatments tend to be limited in their effectiveness.
Merino wool running clothes for cooler temperatures.
Merino has the added advantage of being extremely odor resistant and does not have a synthetic feel. Wool running clothes can be worn multiple times before odors start to develop. As well, when Merino becomes damp is still maintains its warming ability (similar to a wetsuit effect). However, in extreme perspiration merino clothes will become excessively saturated and heavy. If you're not a heavy sweater than Merino is an excellent option - there are now thin ultra-light merino fabrics that have exceptional breathability and work well even in hot climate.
Wrap a measuring tape around your hip bone line, making sure the tape is parallel to the ground. This measurement determines your waist size. IMPORTANT: Do not rely on your jean size measurements. Just because your jean size is 34 does not mean your waist is 34 inches. Usually, your waist measurements are greater than your jean size.