I have brought up the idea of having an insulation option that does not require a captive shell, with fleece being the obvious first option. Of course, it is not the lightest, nor the loftiest material. The basic idea is that you are carrying a perfectly good outer shell if you have a windshirt or rain shell and adding polyfill or down layers adds two more layers of shell fabric.
I ran across a US Army ECWS Gen III fleece jacket today in a thrift store. It is the fist time I had seen one up front and I think it is an interesting cold/wet weather option. The fabric is like the "monkey man" jackets offered by several manufacturers like Marmot, Patagonia, and Mountain Hardwear. It is a thick, loose, "hairy" kind of fleece, providing a lot of loft, with loose fibers inside and out.
It is heavy– 21oz in a size XL long. It could be considerably lighter using UL construction techniques. There are velcro patches, pockets, a heavy zipper, and nylon reinforcement panels and a loose cut that bring the weight up.
The example I got is made for military use by Peckham. There are a number of different companies making the same under government contract.
See http://www.adsinc.com/gen-iii-ecwcs-level-III for a good breakdown on this jacket. The fabric is Polartec Thermal Pro, with Power Dry (AKA Patagonia R1) side panels— pretty sophisticated stuff for $12 :)
Weight is an issue, but I think this stuff would be great for cold, wet conditions. Add a windshirt or rain shell and you have some warm stuff. I think it would be great to sleep in.
FYI, there is a 300W fleece version out there too. I've had one for a while, but never used it on the trail. Great around town when the mercury drops.


