One key feature distinguishes a jacket from a parka—and it can make a tremendous difference in warmth, especially if you're tall.
The terms "jacket" and "parka" get thrown around a lot in product names, catalogs, and other marketing literature. Though there are no hard-and-fast definitions of the two terms, the primary difference usually boils down to one thing: length. Jackets typically reach only to your waist. Parkas extend further to cover some or all of your butt and upper legs.
Given that parkas insulate more of your body, they are generally the warmer option. This is especially true if you're tall or long-waisted (as in, you have a disproportionately long torso for your height). If you fall into this category, you've probably noticed that some jackets just don't extend far enough to full cover your torso. This is especially noticeable (and irritating) when you lean forward, since a shorter-length jacket will lift up to expose your lower back to the cold.
That being said, parkas do have some drawbacks. The lower hem of a parka can be more difficult to fully seal, an
important feature for retaining body heat and preventing cold air from
entering your clothing system below. The extra length adds weight and bulk, a consideration for winter hiking or backpacking. If you're mountaineering or climbing, parkas can make harness and rope work more difficult. Plus parkas are typically more expensive than their jacket equivalents.
For nearly a decade now, my go-to ultra-warm jacket has been the Mountain Hardwear Sub-Zero Down Parka. (Mountain Hardwear redesigned it a few years ago. Its current incarnation is the Chillwave and retails for $375.)
Parkas are much less common than jackets, but well worth the effort to find. These days, my top choice would probably be the Montbell Mirage Down Parka ($349, pictured).
“Equipped” is an AMC Outdoors blog, written by Matt Heid.