I bought one of these, and then liked it so much bought a second one a week later and another one as a Christmas present for a friend!
I wear this product for two of my favorite sports: cross-country skiing and cold-weather biking.I use it as an underlayer on very cold days, and by itself under a windbreaker in the fall and on warmer winter days.
What I like is that it is lightweight and comfortable, yet keeps me warm. It wicks off the sweat during a hard workout, which is important because clothes that don't do that make me feel cold and clammy in the winter.
I have several Isis products and all are of excellent quality.