Since Spring means 40s and 50s here in Vermont, I'm all about throwing on a thin, long-sleeved layer over my tank top for the first part of my run, especially on chillier early-morning outings. This Ibex Indie Full Zip Long Sleeve ($110) is made of merino wool, so it's warm, wicking, and super-thin and -lightweight. It has a full zipper, so it can be easily slipped off and tied around my waist when things start heating up. It keeps my neck protected from the wind, and the thumbholes prevent wind from going up my sleeves. Another bonus it that it washes well, and I love that it's fitted but not tight. Simple, flattering, and versatile — it'll be a great layer for Winter runs as well.
— Jenny Sugar, contributing editor