What's the best wool for summer clothes?

Merino wool is what you're looking for in summer, because it breathes really well and regulates your body temperature without making you sweat like crazy. It's lighter than traditional wool and has fine fibers that don't itch your skin, so you can actually wear it in the heat. A solid alternative is camel wool, which is also cool and really breathable, but you'll find fewer pieces in stores. Avoid thick wools like heavy merino or coarse virgin wool though - those become really uncomfortable in summer.

The weight of the fabric matters more than the fiber itself - a 200-gram-per-square-meter merino in summer is really comfortable, but a 400-gram one you'll never take off. What I haven't seen mentioned before is that merino wool, even if breathable, still has a density that never beats linen or cotton for dry heat; but if you're someone who sweats a lot, merino stays superior because it dries fast and doesn't smell after three hours.

When I have to wear wool even in the heat, I do better with blends - merino mixed with silk or linen - rather than pure merino. Pure merino weave, even if it's thin, still itches a bit on my skin when it's really hot, whereas with a 70% merino 30% silk blend it actually breathes and doesn't give me that feeling of "I'm wearing wool anyway." Try looking for that kind of blend, it's not super easy to find but it makes a huge difference compared to merino on its own.