We had alot of new guys show up with Underarmour t-shirts while working overseas.
I refused to let my guys & gals wear them while on missions outside the wire.
One, they melt in a fire and stick to skin. Bad idea in a burning vehicle.
Two, though this is a personal choice is they are hot in hot weather unlike cotton that will breathe to a limited degree.
Three, when you put a pot bellied, 300 lb, 50 year old man in a body fitting t-shirt.....that is just an image I do not want in my head again.
Camping around the states they are probably okay especially in cool weather.
DC