As a long time, active outdoor user of all manner of technical apparel including all the synthetics, and way back when, wool, I am amazed at the performance of the merino wool Smartwool Microweight T-shirt. I have been a big fan of Smartwool socks for years but assumed wool shirts would be to warm. I was wrong. The Microweight wicks superbly, wasn't hot in warm weather and because of its very fine knit was very comfortable all day. And most amazingly it doesn't accumulate odors as synthetics do.
In fact, I did a little test last week. I wore the shirt for 3 days straight including 2 long trail runs and work (with a real shirt over). It was as fresh feeling and smelling the first day as the last even after a long plane flight home. I did have a spare T-shirt, just in case... The nickel stripe color is even very stylish and the shirt can easily be worn alone. I am now convinced micro weight merino is the ideal, all purpose material for everyday, travel and vigorous exercise.
And, given that wool does not melt or burn as synthetics do, I think it is safer for military and industrial uses where fire is a risk. In fact, the Marines have just recently banned most synthetic underlayers in frontline situations due to burn injuries from melting synthetics.
The only downside is the price at $50. However, most people likely could make due with 3 times fewer T-shirts, as I did,and save wash energy and water!