Stacking two insulation (puffy) jackets for cold winter conditions

I’ve done something similar with fleece layers as an inexpensive way to add warmth. I have a snug fleece sweater and a loose fleece sweater. The loose one is also thicker. I can switch between the two or use them both (to be really warm). You gain a little warmth with the layering itself, especially with fleece (you trap some air between the layers). I also have a rain shell to put over any combination. I still use this around town. It offers a lot of flexibility.

Since cost isn’t a big issue I could see the same approach by using down or synthetic insulation. So basically a tight fitting puffy jacket and a loose fitting puffy jacket to put over it. They could both be down but consider synthetic for the inner one. There are a few reasons for this. A high quality synthetic insulated jacket can approach the effective weight/warmth ratio of super-thin down jackets because it doesn’t need baffles (if it the insulation comes in sheets). Another consideration is moisture. If you have a big puffy jacket then you probably won’t break it out until it is below freezing. In contrast a lighter-weight jacket could be used when it is a few degrees above freezing and wet. Of course you have a shell over it but you are still bound to get more moisture running through it (especially if you are exercising vigorously). There is a third advantage and that is that compression matters less with the smaller jacket.

So I could see a base layer T-Shirt (wool or synthetic) along with a lightweight synthetic puffy jacket (in your size) and a puffy down jacket a size or two bigger. I have an Oware synthetic puffy hooded pullover. I’ve used it as my only insulation for summer trips (it works just fine under a rain jacket and is lighter than fleece). I could easily see putting a down jacket over it. (I haven’t done that because I don’t do any winter camping. When I cross-country ski I am less concerned about weight and just use a fleece sweater along with a down jacket.) I’m pretty sure that Oware no longer makes that pullover. It may be difficult to find a high quality synthetic puffy jacket — you may be better off with two layers of down.

Absolutely do the stack! It almost doesn’t matter what the layers are as long as they’re large enough to create dead space between them without allowing a bellows effect when you move- bottom drawstrings instead of elastic.

My snow camping go to is: Patagonia Cap Air (RIP I guess?) that’s tight, then loose fitting 200 weight fleece, then Sherpa 850 down parka (quite large,) then if it’s really cold adding the comical MH Stretchdown Poncho over the top. You can modulate heat and cold really nicely by strategically unzipping and forcing some air exchanges through the layers, and I like the double breathable layer to start so you can always strip down to non-clammy layers. My alternative extreme-cold outfit is the same first two and then throw my Montbell Permafrost Parka over those, but that’s for the -30s. It’s such a beastly layer that it honestly doesn’t get the usage it should!

I also think a massive differential in air permiability between the various layers is important- I want my puffy insulating layers to have zero breathability so the warm air that gets trapped can’t get sucked away by gusting winds. It’s actually why I like my DAS light and feel like it’s warmer than the weight would suggest- it’s a size larger than is fashionable, so when it’s zipped up tight and bottom snugged it acts like a thicker puffy because the gap between me and it gets warm and stays warm!

I agree with all Devin’s points. It is a good approach.