I love intense outdoor workouts, even in the dead of winter. What I don't love is gearing up for them—if I dress warmly enough to keep from freezing when I first head out, I'm bound to overheat once I really get going. So what's a girl to do? The answer: Get herself the new Animagi Jacket from The North Face (TNF).

The Animagi is an interesting hybrid. The front and back torso and collar are made of very thin PrimaLoft, while the sleeves and side panels are made of a stretchy polyester blend. (Most of the fabric used in the jacket is recycled, which is a big plus in my book.) At first, I was a little skeptical. This is one very light jacket (a mere 9 ounces), and I wasn't at all convinced it would provide any more warmth than a windbreaker. With some trepidation, I put it on over a wicking turtleneck and a long-sleeve tech shirt, and headed out into the windy, 20ish-degree darkness of the early morning.

I discovered one of the benefits of the jacket right away: Wary of letting my arms get cold, I launched into a brisker-than-usual warm-up. But truly, from the moment I stepped outside, while my arms were indeed a little chilly at first, my core was perfectly warm. When I finally got my serious power-walk going, I didn't feel cold at all. And when I checked my Fitbit activity monitor later, I noticed that I'd spent more time than usual in high intensity mode (translation: more calories burned). My guess is that this was because I never felt overheated—because when I start to swelter, I tend to slow down a little.

The North Face guys describe this as a jacket for "cold weather endurance activities," and they're not kidding. It's ideal for everything from power-walking to cross-country skiing—in other words, activities that are truly high intensity. Wear it for a leisurely walk or bike ride and your arms and sides will freeze.

Style-wise, it's very flattering, fitted but not too tight. The back hem drops slightly (good for blocking back drafts), and there are nice touches like thumb loops over the extra-long sleeves (so no need for gloves if it's above freezing). It's also very packable; I could stuff this jacket in the corner of a carry-on or workout bag with no problem.

The only thing that bugs me about this jacket is the lack of reflectivity: The only reflective part is the logo, and that's not going to make me very visible to oncoming cars during my early morning workouts. Granted, the jacket has a UPF of 30, so it gives sun protection during the day, but during the colder months, most folks who exercise either before or after work are doing so in at least partial darkness. Just something to think about, TNF guys, if you update the Animagi for next year (and I hope you do).

Regardless, the Animagi has earned a permanent place in my workout wardrobe—at least until spring comes.

Product: The North Face Animagi Jacket

Category: Apparel

Pros: It's the best jacket I've found for staying just warm enough during intense, cold weather workouts—it keeps your core toasty while letting your arms and sides breathe. It's also flattering, comfortable, super-light, and extremely packable.

Cons: It's not reflective.

Cost: $149 at www.TheNorthFace.com

Extra tip: Make it reflective by adding the GoMotion Sport Runner Litebelt, winner of the Best Reflective Device in our 2009 America's Healthiest Fitness Buys.