Merino next to the skin should feel quiet: no scratch at the collar, no smell by Thursday, and enough air that a sweater over it does not cook you.
We wore superfine yarns around 17.5 micron under ordinary winter layers, paying attention to itch, odor, and whether the knit still breathed once you were on a warm train.
Fineness and feel
A lower micron number is softer, and also easier to hole if the knit is thin and you wear a rough backpack. Odor resistance is the reason to choose wool over a synthetic, but a heavy layer worn for a week will still need a wash.
- A fine yarn if you are sensitive at the neck and cuffs.
- A knit dense enough that a bag strap does not show through in a day.
- Flat seams where a pack or a waistband sits.
- A weight you can wear indoors, not only on a cold walk.
The best base layer is the one you forget you are wearing.
Washing it
Cool water, a wool wash, and a flat dry keep the shape. High heat is what turns a good shirt into a crop top. Hang it to air between wears and it earns the days you skip the laundry.
Buy for the layer you already own. A base layer that only works alone is not a base layer.
