I too wear my outer parka/ jacket under my waders unless its pouring rain. And for that reason, I don't really get the appeal of the delta wading jacket as it is an uninsulated rain jacket/ outer shell. Unless you hunt in the DEEP South where you're almost never in temps below 40, then I could see it being useful. Which is why I much prefer the hudson jacket for an outer shell, as it has some insulation and still has the water and windproof shell as the delta, with a slightly longer cut for the torso as well. Which for me makes it much more versatile as I can use it practically all season and only needing to change my layers underneath a little.
