Heat-tech and airism are both incredibly legit base layers. Heat tech is my favorite piece of clothing for New England winters and winter treks. The ultra light down jackets and weather proof parkas are incredibly convenient too.

They seem to be going through a wierd cut phase, which accentuates men's chest in an awkward way and looks like dad wear unless you are really slim/athletic, but I hope it is temporary thing. (or maybe I just need to get in better shape)