The pack frame makes use of your sleeping pad to support and cushion
you from the contents of the pack. You can use just about any type of
open or closed cell foam widely available at any outdoor shop or site.
I would suggest sticking to an open cell foam with a thickness of no
more than 2 cm because it offers the best weight to insulation ratio
(compared to closed cell ones) although with some sacrifice to durability.
You can use
the accordion-type Z-rest compact closed cell foam pad. They are commercially
available in long (fourteen 5" sections) and 3/4 (ten 5" sections).
Both have a thickness of 3/4" and a width of 20" so you may
have to trim it to fit in the mesh backpad holders of the LAB. However,
if you're a really tall person and you made the pack according to your
body dimensions (i.e torso length values equal or greater than 23")
then you need not do any trimming at all. But in most cases, one has
to trim the width of the pad to fit the minimal confines of the backpad
holders. If you get the long Z-rest then you can cut it into two pieces
with one having 6 sections and the other 8 sections. An important thing
here is to fold them accordion-style with equal number of segments per
side before slipping them into the holders. Use the 6 section for your
ultralight needs and the 8 section for more luxurious camp-outs. Remember
though that the longer the pad (8 sections) the harder it is to fit
or put inside the holders and the farther the pack's mass from your
center of gravity (translation: less stable and less comfortable) because
of the thickness of the folded pad. An 8 section Z-rest folded to fit
the LAB pad holders would have a thickness of 3" - that's quite
thick. I encourage using the 6 section pad with a folded thickness of
2 1/4" instead.
But if you
can find an open cell foam pad with a thickness of about 5 mm and cut
it to a 30" length (the width varies with the packs size), then
go for it.
30" long x 14" wide x 5 mm thick and I folded it twice to
have a sort of 3-section arrangement before slipping it into the holders.
It weighs a mere 1.8 oz and can insulate my head, back up to my waist
area from the cold, damp ground. The following illustration demonstrates
the type of pad set-up I use for the pack's frame.