I sweat - a lot. Especially if I'm carrying a backpack during the summer, my whole back is just one wet spot. A cotton T-shirt is a big no-no, when one gets wet it'll be wet and clammy for the rest of the trip. I tried the technical shirt kind and while they do dry fast, I'll be freezing while it's doing that.

I discovered merino wool T-shirts about a decade ago and don't wear much else - except for a few nerdy print shirts on occasion.

Merino wool is cool even when wet and dries really quickly. It's also pretty much self-cleaning due to the lanolin (a type of fat) in the fibers, and smells don't stick to it for the same reason. Even after the sweatiest hike, I can just hang it out to dry and it's good to go.

I can go on a week's trip with just two shirts, alternating them on different days.

If you do wash a merino shirt (which you shouldn't do too often) always use a wool detergent that has lanolin in it.

And all of the above goes for all other merino garments. I've got a hoodie from a merino wool mix that I wear all around the year. It's warm during the winter and not too hot during summer nights, if I get caught in the rain it'll be dry in no time.