I switched all my running shirts to merino and depending on the intensity of the runs and outside temperature (so in fact just depending on how much I sweat) I usually can use one shirt for 3-5 runs before I need washing it. Just hang them outside to dry and air over night. Saves a lot of water and detergent and they are so much more comfortable and functional than any synthetic fabric. I also have an old nike polyester shirt which starts to stink after 30 minutes of use…