quality base
Nice quality base layer that breaths well and gets the job done for hikes with cool mornings but warm day time temps. great for shoulder seasons in the northeast

One of the best base layers around!
The Patagonia capilene line is awesome. They haVe four different types of capilene; each for a different weather condition and temperature. The capilene 1 is the lightest. It is made of 100% polyester, which dries very fast. However, the texture and feel is almost exactly like silk. I take an xl, and I feel like It fits me very well. Most t shirts that I have fit me like a pup tent, meaning they fit ok in the shoulders, but are much too wide around the waist. The capilene 1 fits so much better, so if I don't tuck it in, it doesn't flap in the breeze. Even though the fabric is thin, it is very durable. As I read the reviews, it sound like most people prefer the cap 2 above the cap 1. However I like the cap 1 better. The reason being that if I don't shave for a day or two and wear the cap 2, my whiskers sometimes rub against the fabric of the shirt and create pilling under the chin and on the shoulders. The cap one has never pilled, even a little bit. I got most of my cap 1 shirts on sale. Even though I really like them, I'd have a hard time paying full price for them.

light
I used it for climbing to prevent from scratches and sun exposure. Great piece of clothing, feels cool even in superhot weather. Warning: 1 day use max as its synthetic and will stink.

Just what I wanted
I found this Patagonia product, in black, in Belgium. The white version is wonderful. Just warm enough, but cool enough not to overheat. Wore in 30 degrees (-1 C) as my only shirt during a 40 minute run. Perfect.

fixedgearrider
I use the long sleeve crew neck as a summer undershirt. It offers 15-UPF sun protection so I don't need to use pore clogging sunblock. Moisture management is excellent. I feel cooler than with out it. The Texas summer sun is brutal.