I cut my wally world pad from my head to my knees-about the
length of a 3/4 ultralite Thermarest. I have found that when I pack
my clothes in the vacant area from my knees to my feet, that is all I
need to keep my lower extremities warm since this portion of your
body has nowhere near the bearing weight that your torso has. This
allows for double use of your clothes when you are not wearing them.
My torso almost always gets cold before my lower extremities. In
addition, this cuts weight in two ways: the size is smaller of both
the pad and reflectix or any other insulating material you use for
winter conditions. It also makes for a smaller pack.