Most compact UL down quilt or sleeping bag?

[canalligators]

Using a compression sack helps a lot with reducing volume.

[froze]

There is a quilt that can pack down the size of a water bottle about 5" x 6", it's called the Therm-a-Rest Vesper 32, not only does it take up very little space, but it only weighs 15 ounces, and as the 32 indicates its good down to 32 degrees, a sleeping bag that rating is for 32 degrees are actually comfortable down to 42 degrees, but this is a quilt and the temperature ratings are more accurate.  While it's not cheap at $361 for the long version, it's not horribly expensive either.

The problem with stuff that is lightweight is that the fabrics are flimsier and may not hold up as long as heavier ones.

If you want something warmer then the pack size and weight will go up, there is no way around it, but the smallest for a 20 degree back is the Therm-a-Rest Corus Quilt, it weighs 22 ounces and packs down to 7" x 10" and cost $300.

If those two choices are too much for your budget, and if don't need as warm of a quilt there is a third option that is very affordable at around $65 called the Get Out Gear Down Camping Blanket, it weighs just 17 ounces but packs a bit larger than the Vesper, but smaller than the Corus at 5" x 12" not bad size though, but the temperature rating is just 45 degrees which is typical of most blankets, most blankets will be lighter than most quilts, but as you can see, as it is with cycling, the more money you spend the lighter you get stuff, so it will depend on whether or not the money being spent is worth a few ounces, that's where blankets come in, they're cheaper and lightweight.

When using a quilt or blanket you will need a when using a quilt, you will need an insulated mat.

Do some reading on blankets and then decide if that is something for you.

[doubravsky]

+1 on the Therm-a-Rest Vesper. I have the 32 and the 20 degree one.. started with the 32 and then when doing a winter trip- picked up the 20 degree because I really like the 32 and just wanted a warmer option.

They pack really small and light.. and with an insulated pad... do a nice job with temperature.

[davidbonn]

...
When using a quilt or blanket you will need a when using a quilt, you will need an insulated mat.

Generally you should expect to need an insulated sleeping pad of some kind with any sleepingbag as well.

You can usually expect more heat loss from conduction with the cold ground than with radiation or convection with the cold air, so the kind of sleeping pad you are using can have a huge effect on perceived warmth.

People are all different too, and some people have metabolisms like a small furnace anyway and can sleep very warm.  Also if you had a generous hot meal before bedtime (or even three or four slices of cheese and a few pieces of smoked salmon) that can make a huge difference in how warm you will sleep.

A good fleece hat worn to bed and putting everything in a lightweight bivy sack (https://bivysack.com/shop/ols/products/bivysack-drawcord-closure) (even inside a tent) can be good for another 15 degrees on the "comfort rating."  I've managed to sleep comfortably down to 15F with a bag or quilt rated at 32F using those tricks.

For compact and light (and when money is not an issue) I'd probably recommend the Western Mountaineering Nanolite 38F (https://www.garagegrowngear.com/collections/gear/products/nanolite-by-western-mountaineering?variant=44805514461371)

[froze]

All you have to do is google: sleeping bag vs quilt, and see after reading and watching videos which you think would suit your purposes the best.

Sleeping bag temp ratings, for some dumb reason I've never been able to figure out, will say they're comfortable down to 30 degrees for example, but the real temp rating is about 20 degrees warmer!  Whereas with a quilt what they say is what they are!  I don't think sleeping bag companies should be allowed to advertise the temp ratings the way they do.

The sleeping bag I have is a summer bag rated for 40 degrees which means 60 degrees, and I have a Sea to Summit Reactor Extreme that they claim adds up to 25 degrees to a bag, another lie, it might add 5 to 10 degrees at best, I use the liner to protect the bag but on hot nights I just use it as a sleeping bag.  I don't camp in cold weather so I'm fine with stuff I have, and if I get a bit chilly I always pack a set of long underwear, and if that's not enough I can put on my rain pants and rain jacket.  Only once did I have to resort to using all that stuff, when the temps unexpectedly dropped to 38 to 40 degrees in the summer one night?! Weird.  I went to bed the temp was about 68 degrees so all was good, and the weather service said the temps would get down a low of 58, went to sleep and woke up shivering, so I put on all my stuff and went back to sleep.

I also take a wool beanie just in case, which I wore on that one cold night.

[davidbonn]

Everybody's different.  And different companies use different methods for computing the temperature rating of their bags.  So we as consumers are left with not very good information about what sleepingbags and quilts might work for us.

Do not underestimate how important ground insulation is.  The compact light-weight air mattresses that are popular with cycle tourists often have very poor insulation properties, and are often far less effective insulation than a thin (though bulky) Z-Rest style closed cell foam pad.  That ground insulation is just as important in any sleepingbag as in a quilt, because the insulation underneath you is squished flat and useless by your body weight.

I find that a sleep system rated at between 30F and 35F works best for me for summer backpacking and three-season bicycle travel.  But I am fussy about ground insulation, usually am in a bivy sack of some kind, and always carry a fleece hat.  In extreme conditions (like one memorable night where it got to 15F) I was wearing all of my clothes in the bag and was just barely warm enough to sleep.  But I managed and made it all work.