I've tried oodles of base layers and nothing makes me feel better or warmer than my Capilenes. They are an excellent wicking base layer for many different activities including backpacking and whitewater kayaking.
I've hijacked the Patagonia graphic (shown below) that best explains which fabric thickness is best for different activities. It is a very good guide for understanding the relationship between activity levels, outdoor temperatures, and base layer thickness.
I use a Capilene 1 long sleeve jersey and long pants to sleep in during the late spring, summer and early fall. The fabric feels extremely silky and helps keep my sleeping bag free of sweat and body odor. In early spring and late fall, I sleep in a Capilene 3 jersey and long pants for extra warmth. This sleeping layer can be used as a warmer backup to my daytime base layer or if my daytime base layer gets wet.
The weight of the of a Capilene 1 crew jersey (size xl) is 5.8 oz and the weight of the long underwear is 5.9 oz. Both of these garments get packed in the stuff sack used to hold my sleeping bag. The weight of my Capilene 3 crew jersey (size xl) is 8.1 oz and the weight of the long underwear is 7.5 oz.
I often hike in a Capilene 2 crew jersey in the early spring which together with a paclite shell will hold me down to temperatures of about 35 degrees if I'm hauling a 20+ pound pack and using poles.
I have also tried the Capilene 1 short sleeve shirt, but i don't like it. The fabric has a tighter weave than the Capilene 2 jersey and is less breathable in my opinion. It is very easy to snag if you are hiking in brush and tends to accumulate and hold body odor after a day of hiking. If you decide to try the Capilene 1 anyway, I recommend that you get one size larger. They have a tight fitting cut.
Over 50% of every Capilene garment is made using recycled polyester and Patagonia will accept used clothing for recycling. Of course, you have to destroy it first, and that seems unlikely. These clothes last and last.
Disclosure: The author owns this product and purchased it using their own funds.