I needed an insulator under my Gore-Tex 3L shell ski pants and I was lucky enough to find this Spyder Glyssade Insultor Pants. I had it for skiing in a 10 degree Fahrenheit weather, and I was not cold at all.
It’s toasty warm to wear around the house. I also had it on by itself, when it was 25-30 degree outside, and it kept me warm. Overall, I would recommend this product.