Mine is definitely an ultralight sleeping bag, but it actually
weighs 19 ounces with the stuff sack. Stuff sacks aren't always
necessary, however. I can just stuff it directly into my pack
or put it in a half-ounce bread bag. It is a down sleeping bag,
the Western Mountaineering Highlite. (You can see it in
the video further down the page.)
It appears to be very fragile, and I have babied it over the
years, but it may be tougher than I thought. I have used it from
sea-level to 16,000 feet in all types of weather (I camp under
a tarp much of the time), and it still has all of its loft and
appears new. The zipper only goes half-way down (to save weight),and
it is a mummy bag, but it has always been comfortable for me
(I'm 6'3", 165 pounds). There is a full description at the
bottom of the page. At the time I bought it I couldn't find any
lighter bags. Now I see that there are some other options out
there.
A Synthetic Ultralight Sleeping Bag
If you aren't sure you can keep your bag dry (important with
down), a good lightweight sleeping bag to try is the North
Face Propel 40 Degree Polarguard, which weighs only 16 ounces.
That's an amazingly low weight for a synthetic sleeping bag.
There is a complete description at the bottom of the page. Any
good synthetic bag is probably better than down if you are regularly
getting it wet.
A Down Ultralight Sleeping Bag
The Marmot Lithium 0 Degree Down Bag weighs only 2
pounds, 11 ounces. That's fantastic for a true winter bag! I
don't recall ever seeing another 0 degree bag under three pounds.
The other big advantage of any down sleeping bag is it's compressibility.
Nothing packs smaller than down.
Using an Ultralight Sleeping Bag
A note about using an ultralight sleeping bag: Treat it gently.
Usually the lighter bags are more fragile. I have used mine in
snow and rain for years, from Ecuador to California and Michigan,
and it shows no wear. Obviously, if you baby these things, they
can last a long time, and it's worth it. Reducing the weight
of the big three (pack, tent and bag) is what makes ultralight
backpacking possible.