The Vesper Quilt from Therm-a-Rest is rated to 32 deg F (0 C) but weighs just 15 oz, stuffing down to the size of a one liter water bottle. That’s thanks to the 900-fill Nikwax Hydrophobic Down.
Remember, this isn’t a sleeping bag, it’s a quilt, that you wrap up in, so consider it appropriate for three seasons. Or, use it in conjunction with a cold weather clothing system.
One feature that’s pretty cool, is that it will integrate with a Therm-a-rest mattress. Plus, there’s a nice footbox, built-in.
Available in regular and tall lengths, there’s also a model that goes down to 20 deg F (-6 C).
man, down might not be tactically sound many places but being able to get a true 3-season sleep system into a buttpack these days is incredibly tempting. I have a 850 down quilt and an xtherm that will take me below freezing but will almost fit in a sustainment pouch. these high fill-power down quilts are about as far away from an MSS as you can get.