The onesie, or union suit, was an iconic baselayer 150 years before we called any type of undergarments "baselayers." Many of the same pragmatic features—like seamless layering and thermal efficiency—that made these one-piece undies a go-to for a range of users, from Victorian women to American frontiersman, make them excellent cold-weather technical pieces today. Thankfully manufacturers have made some modern twists to make them more comfortable, flexible, and breathable than the original cotton or wool union suits.
Wool base layer one piece.
Capilene 4 EW one-piece suit.
The Airblaster Ninja Suit.
I snagged the North Face Wool One Piece from a photo shoot in August of 2012 and tested it through fall and early winter of last year. I tested the Patagonia Capilene 4 One-Piece and Airblaster Ninja Suit from mid-winter through last spring for our current Winter Buyer's Guide. These are pricey, but for the right applications, they can replace an expensive baselayer system.
The North Face Wool Base Layer One Piece $230, thenorthface.com
The wool-polypropelene blend that this baselayer is cut from made it the itchiest as well as the warmest of the bunch. I was extremely thankful for the added thermal punch when resort skiing in Santa Fe in single-digit temps. It was also an integral piece of gear when I tested drysuits on a 40-degree day in sub 50-degree water. I found it too warm for high aerobic activities in anything above the coldest mornings—but I do run hot.
This is the only one-piece of the three that does not have a hood, which I preferred because it cut down on bulk around my neck.
The single-zipper u-shaped drop seat was the hardest to use and I, in fact, ripped the zipper clean off in a feat of strength as the result of a red chile breakfast burrito emergency while skiing in Santa Fe, NM (sorry if that is TMI).
Patagonia Capilene 4 One Piece $199, patagonia.com
I wrote about the Patagonia Capilene 4 One Piece for Outside's Winter Buyer's Guide because it was my favorite of the bunch. The most impressive feature about this one-piece is its massive temperature range. It was my go-to near-zero-degree skinning baselayer because it was warm enough while I got ready, but did not set me on fire once I got moving at a good pace uphill. This adaptability is thanks to Patagonia's Capilene 4 material made by Polartec—square pillars of loft that are surrounded by thin, breathable channels.
The silver nitrate woven into the fabric cut down on stink remarkably. To test how well it mitigated odor, I did not wash it for a week in which I skinned, and sweated, every morning. At the end of the week the smell was minimal—think one to two days of light jogging in polypropylene. I ended up washing it for good measure.
Patagonia modeled the dropseat after historic union suits—they used snap buttons on top for a quick pull down and zippers around the thigh. This design was the easiest to use of the three.
Airblaster Ninja Suit $110, myairblaster.com
At nearly half or more than half the price of the other two, the Ninja Suit by Airblaster costs about as much as any name-brand baselayer top and bottom you would get at a retail store. It runs the coolest of the three which this was a bonus for high aerobic activities, like skate skiing, on moderately cold days. This onesie is cut from a 96% merino wool and 4% lycra blend that made it stretch like spandex and, in terms of movement, all but disappear when I skinned in it.
The merino wool helped fight odor for a few days of no washing—but was not as effective at cutting down on funk as the Patagonia one-piece.
The Ninja Suit features a drawstring at the waist that I could have done without because it rubbed against my waistline when under ski pants. The drop seat was the lowest tech of the three—a single straight zipper that can open 350 degrees just below your waist—but ended up being intuitive and easy to use.