The Proto Down Top will appeal to minimalists who want warmth for the lowest weight. There are no frills just high quality down in an innovative grid style baffle construction.
Crux says:
A simple, ultra-light style, the Proto Top is a pull-over style. The half-zip has a generous length for easy putting on/taking off, as well as giving some scope for venting excess heat. Likewise, the underarm area has no down insulation to balance heat retention (a kind of body mapping). Half-zip styles are lighter and warmer than their full zip versions, and perfect for anyone seeking to maximise their warmth-for-weight efficiency.
The Proto Top has no pockets. Down fill quality and quantity is 60g (or 2.5 ounces) of 800 fill-power polish goose down. It has a stitch-through baffle construction with vertical stitch lines to further prevent movement of down.
Crux's Proto Down Top is an insulated jacket for the minimalists. The smock style makes this warmer than a a full zip jacket as less zip for heat to escape through. There is no down in the under arms to add a bit of breathability. The absence of hand warmer pockets keeps the weight down. There is a an internal chest pocket which doubles as stuff sack. The cuffs are lycra trimmed to ensure a close fit to trap heat in.
As you would expect form Crux the down quality is very high at 860+ fill power. The baffle construction sets this jacket apart from its competition. The rationale behind the use of the interesting grid pattern is to eliminate down migration to reduce cold spots and less lofting time for the jacket to provide the warmth you need.