Linen, and other natural fabrics will be most comfortable. I usually travel in cotton slacks and T’s with a linen shirt (3/4 sleeves) that doubles as a light jacket. The shirt gets worn almost every day — exception would be Spain and parts of Italy where it’s too hot. Most of your cities will not be as hot (evenings at least) as Chicago. The southern portion of your trip will probably be scorching, but almost every place will cool down a bit in the evenings — some places cool enough that you’ll want something with long sleeves.

Once again thanks Oldlady!

You might give an idea of where you’re going.

Linen would be a waste. High maintenance fabric that wrinkles easily.

I like the dryfit shirts or microfiber. The shirts are like what you use in layering. They are polyester which wicks moisture away from the body and the breeze flows through the material easier so you are cooler. People like to say cotton shirts but they aren’t as porous as dryfit and they soak up sweat which makes the shirt less comfortable. Walmart makes some that are in the men’s section and are very inexpensive compared to Nike.

If you’re worried about being cool at night, (I can’t see that much of a swing unless you change destinations), then get some of the camping pants that have legs that zip off.

Even in the southern portions of your trip, it doesn’t get humid like it does in the eastern half of the United States.

In any case: on warmer days AVOID KNIT. This [i]should[/i] be common sense, but American men frequently where knit polos in the dead heat of summer. AVOID KNIT. Avoid knit avoid knit avoid knit….can’t say it enough.