This is my favorite running shirt for shoulder-season weather. I've found the NuYarn composition to be absolutely perfect for a running shirt: it dries quickly, and has all the great properties of merino wool, but also seems to be more durable. The weight of this shirt is perfect for running. I use it as my only layer on summer evening runs or mid-day autumn runs, and as a base layer under a running fleece for winter running. I run in both the short-sleeve and long-sleeve versions of this shirt, and they're my primary running shirts. I recently ran the Moab Trail half-marathon in the long-sleeve version, and it was perfect for a cool-weather morning run, allowing me to regulate my temperature by rolling up the sleeves when necessary. I would LOVE to see a version of this shirt with a hood!