The Icebreaker BodyFitZONE 260 Zone is a fantastic midweight merino wool baselayer.
The balaclava-style hood looks a bit funny, but it's super comfortable and cozy.
Great for cold running days.
The sleeves have thumb holes.
The shirt comes in a hooded zip, a half zip, and a crewe neck.
The half zip is quite long, which lets you regulate temperature better.
Under the armpit there is a different, looser fabric that creates a "heat dumping zone" meant to keep you from sweating.