Arc'teryx Phase AR vs Patagonia Capilene Thermal Weight Zip-Neck Top

They will fit under a shell just fine since they are next-to-skin.Whether they offer the right level of warmth, depends in what weather and climate you plan to use them in and what activity you plan to use them for. I rarely use them and prefer the old Phase AR when I need to use a base layer bottom under a shell or use the Phase AR and bring along an Atom LT pant which I can throw on if needed. There are exceptions - e

The feather weight is deceiving, in that the warmth factor is very high. The fit is good and it just feels right. All pluses, no negatives for this base layer.

The fit is perfect. It feels like its shaped to your body and unlike other base layers it doesn't seem like its designed for bodybuilders or Ethiopian marathon runners, its a fit for normal athletic people. The fabric is comfortable on the skin and I have had no experience of it rubbing. It looks good too

Bought specifically for skiing but used for everyday under layer in cold. Lightweight, good fit, comfortable. Wanted warmer layer but now have lighter under layer.