I am travelling to Lapland on February and I am getting some clothing I need (I live in a warm weather place). I have base layer pants and rain pants already, and I want to buy a pair of pants for mid-layer. Following your guide (https://www.rei.com/learn/expert-advice/layering-basics.html) I see that you recommend the Patagonia Mahnya Fleece Pants as insulated layer. Why I am afraid of, is because these pants are made of cotton mainly... could the excess of heat evacuation could be a problem here?
Although the Patagonia Mahnya Fleece pants would be a great option for a warm and dry climate, as cotton is lightweight, breathable, and soaks up sweat, allowing heat to escape the body and for you to stay cool, we would not recommend this pant as a mid-layer for cold/wet locations (which Lapland will likely be in February).
Instead, we would recommend that you consider something made mostly of synthetic materials, such as: