Women's Midweight Base Layer

Two hundred grams per square meter is the number to hold in your head, and this class runs from about 190 to 260. Warmth roughly doubles over the lightest class while the cloth stays thin enough to sit under a shirt or a slim jacket sleeve. If you own one base layer set, this is the weight that covers the most days in a year.

Grid construction is the detail worth paying for at this weight. A grid knit builds raised squares of fabric on the inner face with valleys between them. That is why the raised parts hold air while the valleys leave channels for vapor to escape and keep less fabric touching skin. That structure gives the warmth of a heavier flat knit at lower weight. That is why so many technical midweights are gridded rather than plain. Flat jersey stays the smoother option and hides better under close clothing.

Lightweight Base Layers dry faster and leave you cold the moment you stop. Bulk is what Heavyweight Base Layers add, and you notice it at the knee inside a boot. Similar warmth comes from Waffle Knit Thermals, which surrender all of it once damp. Sitting between the extremes is the whole point. It means this class handles a day that mixes walking, riding a lift and standing about.

Ski and snowboard days, winter commutes, cold offices, dog walking below freezing and outdoor work with breaks in it are the cases. Roughly 20 to 40 F is where it makes sense with a mid layer and a shell over it. Bottoms at 200 gsm still fit under straight jeans and work trousers, though 250 gsm starts to show at the thigh under anything slim.

Check the inner face with your hand, since a gridded surface should feel like raised ribs rather than a flat sheet. A brushed finish adds warmth while slowing drying. A hem reaching two inches below your waistband with your arms up matters here, because this is the weight most often worn under a pack. Rotate two sets rather than washing one hard, and wash cool without softener, as the film softener leaves fills the channels a grid knit works by.