Layering quilts and temperature rating.

Matthew,

The ~0F rating value is the correct one for combining a 30F and a 20F quilt. I use a database of my own tests rather than either source you referenced. My simple summary analysis is as follows:

30F quilt 800 fill average = 8.5 oz.
20F quilt 800 fill average = 11.8 oz.
_______

20.3 oz total 800 fill

Average quilt rating with 20.3 oz of 800 fill = 0F

Would air gaps between the quilts be a detriment or a benefit? Depends on how they’re sealed together I guess.

Thanks Richard.

Another question for anyone who has experience layering quilts – did you use a wider quilt for the top quilt? Its less than an ounce and only $5 difference, but I can’t decide if its necessary.

A slightly wider top quilt means there is a little less chance of drafts at the sides. Since you are not in direct contact with the top quilt it can be hard to know at 2 am whether it is over you correctly.

Comment: putting a top quilt over TWO people is even more effective. It means you are sharing your heat output. Sue & I do this when using UL summer quilts at -7 C.

Cheers

• a 40F quilt/bag adds around 20F to the rating … if you go on EE site and work out the down fill on the various quilts this more or less holds true, a few years ago big agnes said the same thing on their site
• you will want on step up in length and width for the outer quilt … if using a bag make sure you get a wider bag (ex. 61″ if yr inner bag is 58″)
• you will need additional headgear if you are using quilts … a simple jacket hood and fleece/wool beanie probably wont cut it at those temps … get a dedicated down/synth hood or a down beanie at minimum

PHD has a good page on combining bags …

http://www.phdesigns.co.uk/what-is-sleep-systems

;)

I’m skeptical of layering purely based on oz of down, because it may assume full loft.  I was talking to George at Loco Libre about it earlier this week as I’m looking for a winter quilt.  He said extra ounces will help keep the down from shifting, but adding too much will keep the quilt from laying optimally.  He said baffle height and the correct amount of down is the thing.  Pulling a quilt tight (or a too small sleeping bag) or adding weight above it would also seem to limit the full loft of a quilt/bag.

It seems to me the loft in inches is the reliable measure.  Zpacks has this (referencing backpackinglight.com): http://www.zpacks.com/quilts/down_loft.shtml.

I guess quilt vendors might have different emphasis on baffle height vs overstuff – not sure if everyone is consistent on what they publish for loft height.  Every baffle would be thinner at the baffle and thicker in between.  Stacking quilts might average this out a little since it should create dead air between the quilts where it’s uneven.  However the weight of the top quilt will probably also reduce the height of the inner quilt somewhat.  Maybe I’m stating the obvious for many.

I’m thinking about getting a new top quilt for hammocking and ground sleeping down to the low teens, and many on Hammock Forums have suggested first using all your clothes, and/or getting a 2nd quilt to take for lower temps (I have a 30F EE Revelation) – as a colder weather stand alone – not supplemental.  The colder weather clothing seems like an easy first step, but I don’t think I can supplement my current quilt down to the temps I’m looking for.  I’m looking instead at a 20F quilt set maybe with an ounce or two of extra down to limit movement.  Then supplement with thicker insulated clothing.  That’s my backpacking strategy.  For car camping the stacking quilt method sounds great, so I’ll look forward to more posts, but I probably wouldn’t design an optimal system – just add more down or wool throws until I was warm.  If winter car camping in a tent you can also bring a propane heater!

(Temperature of combined bags/quilts) = (Temperature of inner bag/quilt) – ((70* – (Temperature of outer bag/quilt))/2)

I asked something similar and one of the conclusions was that thay formula shouldn’t be regarded as a general rule. It works in some cases but that probably will be coincidence.

Let also take you example: with the 20°-quilt as the inner quilt, the result is 0°. With the 30°-quilt inside, the result is 5°. OK, let’s say the warmest bag should always be on the inside. But what if you have then 2 quilts of both 70°. As both are equally warm, both quilts can be put on the inside. Then, whatever you do,  the result will be 70°. Mmmm.

bob

the compression by weight is a minor issue at best … if you were talking about putting heavy quilts on top it may be an issue … but were talking UL thinner synth/down quilts and the weight is quite spread out

remember than manufactureres put ALOT of down in those -40C bags all the time, and they often have windstopper or WPB shells …

also in low temps over time moisture accumulates in the bag if you cant dry it out, and can freeze solid … this adds to the weight …

a synth overbag will mitigate this issue quite a bit and is worth any other potential loss … mountaineers and arctic explorers have been using such for decades

now compression because the outer bag/quilt is too small is a different story …. the outer layer should fit the inner one without any significant compression …

so it needs to be oversized

;)

Bob,

Please look at the applicable academic research or search this site for some of my many posts on the topic of “down density”. Then you will understand what I mean when I say, “I think one of the words in your reference is most telling (George at Loco Libre)”.

Hi Richard,

Searching down density revealed a 2009 post where someone mentioned a comment you had made 3 years earlier.  The 2009 debate seemed multi-tracked and not really relevant to the OPs question.  Neither was my post mostly relevant.  Down density is interesting and I was surprised to hear your conclusion that 2.5x overfill still provided a warmth benefit without penalty to the insulating value of the extra down.  I read some, but not all.

However, in reading up, I also noted the following from Dustin Short in 2012, “To maximize warmth/weight, keep your down as fully lofted while minimizing down shift and cold spots…again usually a 30% or few ounce overfill accomplishes that goal.”  Someone also mention the point I took from George.  The word he used was “drape”, and the possible lack of good drape caused by more than optimal overstuff (as a primary function of weight)   If you meant a different word, let me know.

Like Dustin, I’m mostly interested in the lightest weight option.  But as part of a cost effective system that works over a wide range of temps, and my debate was weather to get a 20F quilt to use most of the time, and stack it with my 30F EE Rev on those rare cold trips, or get a 0F quilt for the 0-30F trips and use my 30F from there up.  I’ve still not decided, but hoping to finalize during the sales this week.

The OPs question may be more academic.  Richard and others have done much more research overs the years than I have time to digest

Actually, Bob, I have a 20* and do plan to layer a quilt over it to make it a winter setup.