I normally use a Patagonia Capilene lightweight long sleeve baselayer as my summer backpacking shirt. I like the wicking and sun protection, but the fabric can feel heavy and clingy in hot weather. I've been looking for a lighter weight, cooler top with a slightly looser fit. This fits the bill. With UPF rating of 15, this won't be as sun-protective as the Capilene, but the nice cool feel of the fabric is worth it.
This review was written in the old system and had content requirements that are different than reviews written today.