Terramar Thermolator II Pant
Some may find these polyester/spandex blend baselayer…
Source: bought it new
Price Paid: $15
Some may find these polyester/spandex blend baselayer bottoms to be a little lightweight for the midweight promise, but they've served me very well down to about 25 degrees. I wear them under a pair of soft shell pants and there's no grabbing or bunching. I like the subtle feeling of compression with no restriction of movement. And they've done really well with the stink factor, which is a plus.
While a lot of people swear by wool, it does come with a price tag. I find these synthetics to be a nice, durable performer with a price tag that makes sense.