The Warmest Base Layer? A Look at One-Piece, Full-Body Options.

A one-piece base layer — also known as a onesie or union suit — seamlessly covers most of your body and completely eliminates the potential for gaps (and resulting chill) around your waist. For extended adventures into bitter cold, it can be a very warm option, though it does come with several drawbacks, including the added challenge of doing your elimination business with a rainbow zipper or drop-seat.

Staying warm is on my mind this morning as the coldest air of the season thus far descends on the Northeast. As I write this, it's minus-eight degrees atop New Hampshire's Mount Washington, with temps expected to drop into the negative teens over the next 36 hours. In the spirit of maximum warmth, here's a quick round-up of some of the best available one-piece options.

Patagonia Capilene 4 One-Piece Suit
Available in both men's and women's versions, it features Patagonia's warmest base layer fabric Polartec Power Dry fabric (made from recycled polyester), and incorporates a drop-seat design operated with two short zippers on either side of the waist. Full-body coverage, including an extended neck collar that can be pulled up over the face. The men's version features a hood, the women's doesn't. $199.

Mountain Hardwear Stretch Thermal Suit
This 'farmer john' style base layer lacks sleeves but makes up for it with extra toasty stretch fleece fabric. A six-slider rainbow zipper provides a range of access options in times of need. Only available in a men's version ($150). 

The North Face Wool Base Layer One Piece 
The spendiest of the lot ($230), this full-body base layer features a mix of wool (33%),  polypropylene (38%), and polyester (29%) and includes The North Face's Flash Dry technology for faster wicking.

Airblaster Ninja Suits
This range of options wins for most entertaining name and includes options in black, teal, camo, and pizza (?!). It features an integrated hood, zipper for men's #1 access, and a unique 350-degree waist zipper for bottoms-drop and squatting needs. The polyester version is one of the most affordable ($109), a merino version runs $189. Also available in women's.

Equipped” is an AMC Outdoors blog, written by Matt Heid.