as the outer garment it will provide more wind protection, but sometimes it's just a matter of convenience- backcountry skiing/snowshoeing I'll often be in just a base layer and windshirt, stop for lunch or a snack, I just pull the puffy out and put it over everything- when I'm ready to go, repack the puffy and I'm on my way
If you are allowing the wind to penetrate the insulation layer, that layer will cool which means your body heat is required to get it warm. It lowers the effectiveness of the insulation.
No hard and fast rule. Puffy is somewhat windproof on it's own. If it's really cold and I'm not sweating it goes base layer, then puffy, then shell over that if I need more warmth. If it's warm and precipitating, then base layer and shell for breathability and to not soak the puffy. If it's warm and not precipitating, then just base layer. It's about managing both warmth and moisture.
Shell on the outside with a puffy underneath will be more efficient and protect against wind and precipitation. If rain or snow is not a concern you could wear a puffy on the outside for convenience, but a shell on the outside will keep you warmer.
shell on outside. thats why its called a shell. the point of the puffy is to trap air and warm it up. if its very windy you will be blowing that warm air of of the insulation. there is a delicate balance of a too compressing shell and a too baggy shell as it has more dead space or compresses the insulation too much.
that being said my go to is a fitted puffy for under shells. and an oversized to throw over shell when stopping to eat and glass.
depends on if you are planning to need the insulation for a long period of time or a short period of time. For glassing—I’d be putting it on underneath the wind protection layer. For a quick break, I’d be putting it on over. If there’s any threat of decent precipitation, I‘d have it on under the hard shell.
The quickest possible way to warm up is to put it on over the hard shell and do something active—pushups, body squats, short hike
I think you'll be hard pressed to tell a difference real world. Ive done both in extreme cold/static sitting in the wind a couldn't tell much of a difference from one dsy to the next. Obviously, if there is precip or brush to deal with, best to have that outter layer on top.
There are pages and pages of debates on this on climbing forums...I'd be interested to see an actual study done similar to how they test r-value on pads.
Like others have said it’s six one half dozen the other but I’ve always wore it as an outer shell so it goes over my puffy. I suppose whatever way it works for you is the way I’d wear it.
Id wear the wind blocking layer over the puffy,if not for any other reason simply for the fact that puffy layers seem to rip much easier and tend to be more expensive, but not always
It just depends on how long you want to stay warm. Shell on the outside will keep you the warmest for the longest period of time. But if you wear the puffy on the outside you might stay warm long enough to serve your purpose. You just need to experiment with your layering a bit to get a feel for the situations you hunt in.