On the morning of December 3, 2025, in a clapboard farmhouse north of Asheville, Margaret Holcomb laid out four baselayer tops on the kitchen table. Two were merino, weighing 200 and 250 grams per square metre. Two were synthetic — a polyester-polypropylene blend and a 100 percent polyester grid.
She had agreed with the editor of this section, against the wishes of her laundry routine, to wear them all winter, on rotation, on hikes between 24F and 38F across the Pisgah and the upper Black Mountains.
The first thing to say is that 30F is the awkward temperature. It is too warm for a heavy fleece and too cold for a single shirt. It is also the temperature at which the failure modes of each baselayer begin to show themselves most clearly.
The 250 gram merino, a Smartwool Classic Thermal, was the comfort favourite for the first hour of any walk. Against the skin it felt warm without being clammy, and it did not stink at the end of the day. Holcomb wore it on a 14 km loop above Mount Mitchell on January 9, in steady wind, and felt no urge to add or remove a layer for three hours.
The same shirt, worn on a steeper day with sustained climbing, was a different garment. By the second hour on the trail to Black Balsam Knob, with the temperature at 31F and a brisk ascent, she was visibly wet at the shoulders and the small of the back. The wool absorbed the sweat, as wool does, and held it. The shirt remained warm but heavy.
The polyester grid, a Patagonia Capilene Thermal Weight, behaved differently. It moved sweat outward fast enough that Holcomb's skin felt dry within minutes of stopping. But it stopped being warm the moment she stood still. On a lunch break at 4,800 feet, in shade, she had to add a fleece almost immediately or she would have begun to shiver.
The 200 gram merino, an Icebreaker Oasis, split the difference. It moved moisture better than the heavier wool and held heat better than the synthetic. On most days it was the right shirt. It was also the one that wore out fastest, with a small hole at the right elbow by February 22 and a thinning patch at the shoulder strap by mid-March.
The polyester-polypropylene blend, a Brynje of Norway Super Thermo, was the strangest of the four. It is a string-mesh garment, with holes the size of a fingertip, worn under a second layer. Holcomb wore it on the coldest day of the test, January 18, when the trailhead thermometer read 18F at 7 a.m.
It worked as advertised. The trapped air did real work, and Holcomb climbed in comfort with only a thin windshirt over the top. When she stopped, the mesh allowed sweat to escape rather than chill her. When she put on a puffy, the system became almost too warm.
The Brynje is not a beautiful garment. It looks like a piece of fishing net, and on a tired hiker at the end of a long day it carries a faint, unmistakable smell that no amount of weekly washing will entirely dispel.
There is also the matter of stink. Wool wins this comparison so clearly that the synthetic camp should stop arguing. After three full days of use without washing, the merino smelled like a person who had been hiking. The polyester smelled like a person who had been hiking and then sealed in a plastic bag.
On durability, the synthetics win. Holcomb's Capilene shirt looks at the end of the season exactly as it looked at the beginning. The Oasis is on its last winter.
On price, the synthetics also win. The Capilene grid is roughly 95 dollars at full retail. The Icebreaker, comparable in weight, is 130. The Brynje, oddly, splits the difference. The Smartwool 250 is the most expensive at 165.
What this means, after a winter, is this. For a single layer worn day after day for a week with no laundry, merino is the right material. For a single intense climb followed by a cold stop, synthetic is the right material. For a sustained cold winter day with stops and starts, the Brynje string mesh, awkward as it is, was the most adaptable shirt Holcomb wore.
She has settled on a small wardrobe of three. The Icebreaker 200 for most days. The Capilene grid for hard climbing in single digits. The Brynje for the coldest mornings, with a wool button-up over it, which is the combination her grandfather wore on the Bull Mountain trapline in the 1950s and which, as she notes with some irritation, she has reinvented at a cost of roughly 240 dollars.
On the question of which material is better, she will not give an answer. On the question of which is better for a given day, the trailhead thermometer and the elevation profile will tell a careful hiker more than any review will.
Field Lantern will revisit baselayers in a high-output context next winter. For now the four shirts are folded in a drawer, smelling, mostly, like wool.
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