Let me start with a "warning". Those are my first thermal pants , so I cannot compare them to other brands.
They keep my legs warm in Seattle, however I'm not sure how good they are in harsher climates. At first the fabric looked and felt a little bit awkward but I soon got accustomed (maybe all the thermal garments are made of this ribbon ed fabric?)
After wearing them a couple of weeks they look ok, somewhat loose and pajama style. After two laundries they didn't shrink significantly at all.
I am 1.64 m tall and weigh 55 kg and I find small size ok.