Definitely a "base layer". I live in a warm climate and was hoping to get a breathable long-sleeve top to wear for outdoor workouts during the summer - protect my skin from UV without having to wear a lot of sunscreen while also staying cool through sweat-wicking fabrics. I purchased this top in... 3 different colors on sale. I've worn the grey and light blue, and they held up well on jogs. They did show sweat stains, but the thin fabric seemed to help evaporate a lot of moisture so I didn't feel clammy. The white, however, is VERY thin and see-through. Like, the mole on my stomach is clearly visible through the shirt. I think it would become transparent with any kind of sweat, which I am uncomfortable with. It's a good price, soft feel, and complimentary design for my body, so I'll still keep it, but for non-sweaty activities and for layering with a cute vest during the winter. I'm also concerned about the thinness of the material because I train for half marathons and hike, and often wear a hiking backpack or running vest for longer distances. I machine wash but hang dry my athletic tops to help preserve the fabric, but after only 2 washes, I've noticed some slight pilling starting under the arms of one shirt. I don't think it will hold up well when battling the friction of a running vest or backpack, but I'll continue using these for less taxing situations.