Smallest packing 30-40 degree bag

western mountaineering Highlite or Summerlite bags. Both stuff to 6 x 11.5. I wouldn't over compress any down bag.

I love mine. They say it packs to 6" X 10". That is without even using a compression sack, but at that size who needs one.

It packs tiny, weighs 1 pound 1 ounce, and is very conservatively rated temperature wise. I found it comfy with no extra clothing down to about freezing and with some clothing much colder. I have found it MUCH warmer than the cheaper 32 F rated bags I have used. With 2 pairs of socks, bike tights, and a thin pile top I have been comfy at 18F and could easily go colder with a bit more clothing. I do tend to sleep warm though.

I think the EN ratings are Comfort Rating: 41° F / 5° C and Comfort Limit: 32° F / 0° C.

I'll second the WM Highlite and Summerlite suggestions. I own a Summerlite and also own a MYOG highlite converted to a quilt. The Summerlite packs small and the highlite quilt disappears – its quite spartan though and requires back sleeping.

My friend has a Nunatak that looks like it would compress smaller than the Summerlite. It's only partial zip and is cut pretty trim. I forget which model.

Edit to note that his Nunatak is a bag, not a quilt. In case that's important

thanks guys i have a WTB ad up for a WM bag. We will see what happens. also going on the hunt for a phantom 45 for a spare

If you're bringing a hat anyways, you might want to look at Z-packs' offerings. I have one of Joe's 40-degree bags with the regular 900-fill down in the long, wide size, with the standard 7D inner/Pertex Quantum outer, and it still packs down into his 5" diameter, 4L "slim" dry bag, only using about 10 inches of its height. If you get one of Joe's less-generously-sized sleeping bags, I could imagine them packing into something about 2-3L in volume…

Another bag rarely mentioned is the no longer made 14 oz 850 fill Western Mountaineering Linelite. (google it)

The bottom has a drawstring closure and the top has arm slits…meaning you can wear it like a parka. I added arm closures to mine for a little extra warmth while sleeping. Still, the weight is only 15 oz. I open the bottom on hot nights to vent my feet. It has no hood or zip. Due to the arm slits, the top 1/4 can be folded down on hot nights and to make ingress/egress easier.

I don't sleep as warm as I used to but it's been perfect for me down to ~45 degrees with only light fleece. Others might be fine down to 40.

Awesome little bag. Love mine. You might be able to find a used one if interested.

The Montbell Super Spiral #4 is rated 40F comfort and 30F lower limit. It weighs in at 1lb 6oz and packs down to 5.5" X 11".

I had the earlier version of this bag, the Super Stretch, and it definitely packed down small. If the temps dipped down though, it was cold. Overall, it was a well made nice summer bag.