Insulating Layer

So, I was looking through my house for some good winter clothing so that I could spend as little as possible filling in all the gaps in my camping wardrobe. While searching, I found an old Wool Hunting Jacket of my father's. He let me have it and I was excited. However that got me thinking, what is the best fabric to use for the insulating layer? I am thinking its wool, but maybe its fleece...? I am nt an expert on clothing so anyone who could point me in the right direction that would be great.

Also, I have been looking n campmor for good deals and they have some fleece long underwear. I thought fleece was for a middle layer...is fleece a good base layer also or am I not fully understanding layering?

Unless it's below zero, when I think base layer, I think thin, wicking, breathable. Polypro, silk, something like that. I have a pair of midweight fleece drawers and IMO they are almost always too warm for active outdoor sports.

Wool works fine, but poly fleece is a great mid layer. Keep in mind there are different weights of fleece too. You can choose a weight that matches the outside temp. best.

I am using-up old but good stuff. f_klock is right about the thin wicking layer. I bought a set and it has been great. That is my only concession to the "modern era"- for the moment. After the thin layer, on goes a lightweight pendleton wool shirt, then a heavier woolrich wool shirt, then an old 60/40 parka. A wool cap on the head and thisulate gloves on the hands, and I am ready to go for hours in the local hills. Of course, thin layer rei sock under old time ragg wool socks. I am not glorifying the olden days, only saying you can use your Dad's coat and many other closet items made of the right materials. Just be sure to experiment with the layers.