insulating layer for an AT Thru Hike

I have both the Mont-Bell Thermawrap (2005 model) and a Patagonia Micro Puff Pullover (2006 model) and do a lot of hiking on the AT. Both have their advantages but for March on the AT, I use the Micro Puff. It is heavier than the Thermawrap, but warmer. Both are very high quality. I also have and use the Mont-Bell Thermawrap Pants, although I would rather have the similar lighter, BMW Cocoon pants.The Mont-Bell Alpine Light Down jacket would also be a good choice, but I have no experience with it.

martin i have the alpine jacket and its light warm and stuffs down pretty small. pockets inside and out with elastic wrist bands

I like the Alpine Down better than the Down Inner simply because of the elastic waist. It seals in the air better. Of course they are two different beasts. I can't remember if the Thermawrap has the elastic or not.

I've hiked Virginia & PA on the AT in March and I'd go with a Thermolite, Primaloft, Climashield, Thinsulate or other good synthetic filled jacket over any pile jacket.

The pile jackets are much heavier and bulkier than the equivalent warmth of fiber filled/quilted jackets. I have both and know the difference from years of deer hunting and winter camping plus teaching Army ROTC cadets winter survival in the field.

Eric