A puffy jacket can be compressible, it can be warm, and it can be water-resistant—but never all at once. Call it the iron triangle of insulated outerwear: Improvements to any two of these properties must come at the expense of the third.

This classic problem stems from the material properties of down and synthetic insulation. When down gets soaked, it loses its insulating properties. Synthetics stay warm when wet, but they don't compress as well as the natural stuff.

A new synthetic fill from Patagonia confronts this conundrum with admirable results. The insulation, which Patagonia calls PlumaFill, looks like a miniature feather boa, with innumerable polyester tufts emanating from a long, central spine. Those fluffy offshoots compress like down, but stay warm and lofted when wet. Anchoring them to a single strand keeps the synthetic plumes from shifting and clumping inside a jacket, maximizing the insulation's efficiency and helping prevent the formation of cold spots.

Patagonia

Patagonia's Micro Puff Hoody, available starting today, is the first product to incorporate the company's fancy new down alternative—and it's an impressive piece. The windproof, water-resistant shell uses lighter ripstop materials that other jackets in Patagonia's lineup, and a lot less stitching, too. In fact, the Micro Puff completely abandons the baffle construction commonly found in puffy jackets. Instead of confining its insulation to a bunch of little rectangles, Patagonia's designers used lines of strategically placed stitching to guide strands of PlumaFill throughout the jacket's interior.

The result is an eminently packable piece with a higher warmth-to-weight ratio than any jacket Patagonia's ever made. A size medium Micro Puff compresses down to the size of a 1-liter Nalgene; weighs just 9.3 ounces; and offers almost as much warmth as Patagonia's popular Down Sweater Hoody, a 15.1-ounce jacket that uses real goose down for insulation. The new Micro Puff Hoody is not only lighter than Patagonia's Ultralight Down Hoody (the Down Sweater's lighter, svelter sibling), but warmer—a fact that will lead Patagonia to phase out the latter from its product lineup in the coming seasons.

All that light-weight performance will cost you (we are talking about Patagonia, here), but maybe not as much as you'd think. The Micro Puff Hoody sells for $299—which, while not cheap, is $50 less than the Ultralight Down Hoody it replaces. A synthetic jacket that's warmer, lighter, and less expensive than its down-insulated predecessor? Now there's an iron triangle we can get behind.