Logical evolution of quilts?

Interesting idea. The only problem I see is: when cinching things up for maximum warmth, your clothing layers worn under the quilt may very well end up soaked w/ sensible or insensible perspiration — probably in excess of the ‘water weight’ you’re trying to avoid in the bag. VB’s work best with little more than a base layer underneath, which partially defeats the versatility of the variable girth design.

if temps are warm enough to vent the quilt, then that limitation too is less of an issue. But at the fringes, when you’re trying to squeeze utmost efficiency out of your system anyway, you may just be displacing (even worsening) the effect elsewhere in the system. I don’t know, however. A vb fan might have to chime in here. Probably depends on the conditions anyway. Maybe try sleeping in your rainwear (quasi-vb) in condensation-prone weather.

I would agree with you if you are planning on expanding the temperature rating of the sleep system with high loft down clothing. In fact, I have also taken this route with a down sweater. However, if you were to use some ultra-light synthetic layers (like a Montbell vest or sweater) there would be less material to wet-out and dry in the morning (that and you can keep the clothing items outside your pack since you might be using them for layering but you sure don’t want to keep a wet-out bag outside your pack as it serves no purpose but to dry-out.

You’d probably have to really dial down the system but my theory is you can go with lighter synthetic insulation layers + VB quilt vs light high loft down insulation + non-VB quilt and achieve the same comfortable temperature rating. You will also have a more logical drying regimen in the morning (drying out the lighter weight insulation instead of the bag).

I haven’t tried it but the logic seems reasonable.

Sounds plausible, tho I’ve avoided vb’s so far for potential complications above. Yes it would definitely take extra attention. At the very least, I’ve considered pairing BMW’s upcoming synthetic Arc-X (11 oz claimed) w/ Cocoon pants & pullover sans vb– roughly equal wt to a down Arc Alpinist. A “vb+down w/ synth clothing” system gets at the same problem from a different angle.

Be sure you have a nice thick DRY pair of wool sleeping socks if you plan on using a vapor barrier with your quilt. Your feet are normally kept excessively moist all day while hiking, and they need a chance to dry out at night. Otherwise, you’ll get trench foot. The socks should be wool, rather than down or polyester, since you need something to absorb moisture and only wool and cotton do that effectively.

The big advantage I see with vapor barrier in a down quilt is that you can then pull the quilt over your head and conserve your respiratory warmth. I often do this with my non-vapor barrier polarguard quilt (used only at temperatures above 20F) and it has an amazing effect on keeping me warm. I would never try this with a down quilt without vapor barrier, since the down would absorb way too much moisture.

I think that if you try to use a VB in your bag or quilt in nightime temperatures of higher than the low 20’s, you will be pretty uncomfortable. For many of us who use VB in bags, it’s when you enter the range of lower temps. that a equilibrium between the production of body moisture and the humidity within the VB is reached (or so VB theory has it). Ideally, this means you are relatively dry—not swimming in moisture. In higher temperatures, it’s positively greenhouse city.

Granted that you could vent a lot of moisture w/ a quilt setup but it would still be pretty clammy.

Is the condensation coming from your body moisture or from ambient conditions outside?

If from you, I would sleep in appropriate baselayers
and sox and not breathe into the inside of my bag.

If from exterior sources, try a bivy over the bag or pick sites where your shelter can be vented better
(to pick up breezes and avoid microclimates where
condensation is more likely).