There is nothing that prevents compression, however, the pad
(moisture handling pad (MHP)) is a denser foam than the foam that
makes up the bag. It's important that the MHP allows the moisture
through, otherwise you would find the ice building up in your
sleeping bag cloth, then the foam of the bag, and then you are
The system works. -4F in the 1/2" foam clothing and the bag in its
Winter configuration, no tent, no cover, just laid out on the snow
with a ground cloth under the pad. Slept warm and well.
The weight of my bag in its Winter configuration is 9lbs. Expect
heavier loads in Winter. The liner, which can be used as a Summer
bag is just under 3lbs, making the outer bag at about 6lbs for the
Fall, Spring and cooler weather. (Just last week, I used the 1"
outer bag in 38F weather with sweats and t-shirt. Slept fine in my
hammock with the pad under me.)
I hope that helps.