The right fabric, good dimensions, solid design. My go to bivy for alpine climbing and seriously foul wet/cold weather tarp camping in the cold.
Condensation is seldom a problem, unlike any ****-tex bivy I’ve tried, and it even does better than Epic bivies (it’s just not as light).
The downfalls of the South Col: waterproof zip technology still suffers – zips are high quality and weatherproof but pull too hard, and they could be lighter. Hard to argue with much else.