This is by far the best lightweight base-layer I have ever owned. I have a large involvement with many of outdoor sports, pursuing Rock Climbing each week.
I find the RAB Aeon especially useful for climbing due to it's relaxed fit there is a large range of movement available, unlike that of other base-layers tees.
Also, due to it being extremely lightweight it is the perfect tee for hiking and expeditions also, perfect to wear on its own in hot weather and is perfect for adding onto the technical layering system. Due to it being so thin it only takes up a small place in your rucksack!