Women's Lightweight Base Layer

Silkweight names a weight, not a fiber, and the confusion costs people money. A silkweight base layer is usually polyester or merino at 120 to 160 grams per square meter, and most contain no silk whatever. Read the gsm figure and treat the word as a size marker for cloth thickness in the same way denier works on hosiery.

Thin fabric does two things at once. Sweat crosses it quickly, because there is less material to travel through and a shorter path to open air. So this class dries fastest of the three. Warmth stays low for the same reason, since a thin knit holds only a thin film of still air. Expect it to add a few degrees of comfort rather than to keep you warm on its own.

Midweight Base Layers roughly double the trapped air and turn into the layer you can wear alone under a shell. Heavyweight Base Layers are built for standing still and will drown you at this activity level. Silk sits at a similar thickness and costs several times more for a different feel. Nothing else in the family suits a hard uphill effort in 40 F weather as well as this one does.

Running, cycling, uphill hiking, court sports outdoors and any work that keeps your heart rate up belong here, along with warm-climate winters where the temperature rarely drops far. Layering is the other use, and a 150 gsm top under a 250 gsm one gives finer control than a single 400 gsm piece, since you can take one off. Hot sleepers use it as a camp layer where a heavier set would soak.

Hold the fabric up to a window before buying a pale color, because at 120 gsm many knits read as semi-sheer and a light top worn alone will show what is under it. Fit matters more at this weight than at any other. The fabric has to touch skin along the arms and back or it moves nothing. Pilling starts early on thin merino, and a nylon content of 12 percent or more is what holds it together. Cool water and a flat dry are all it asks, and two seasons of hard use is a fair expectation rather than five.