Synthetic Overquilt?

[Edward John M]

You would need two surplus ponchos to sew up a decent overquilt and that would come close to the cost of something lighterin DIY

[Opogobalus]

To retouch on my last comments earlier ponderings:
Order of layering and compression

Obviously with most of these set ups it’s a lw synthetic quilt going over the top. Most people have a 20-30f down quilt.

But, let’s say you were building a system with this layering idea in mind.

A lot of people (not all) agree that a sleeping bag is better to deal with in sub 20f temps.

In warm weather a quilt is definitely more ideal.

Yet for overquilt to work you need an oversized summer quilt. Killing the weight savings.

What if you used a sleeping bag at 20f and a quilt for 40-50f?

You could put the summer quilt inside, and have the some benefits of a quilt and a sleeping bag for your deeper winter option. You have full enclosure with the bag, which minimises the down sides of the quilt, and probably making a far more viable winter option. But you still save weight with the summer quilt layered inside as you don’t have the back insulation. But now your heavier insulation is on top – does it mean your summer quilt insulation is being too compressed by the heavier weight insulation?

You could the summer quilt over top would it be less essential to be oversized with the mummy bag underneath?

Ignoring type of insulation etc.

[Jerry Adams]

https://www.warmlite.com/vapor-barrier/

talks about vapor migration in cold temperatures and refers to some arctic expeditions, for example

“Will Steger used a breathable sleeping bag for his dog sled trip to the north pole. Those 17 lb. bags (almost as thick as our 4 1/2 lb. Goose Down bags) were carried loose on top of sleds ‘for best drying’ yet weighed over 52 pounds in a few weeks from sweat condensing to ice. Luckily, they were flown out from the pole. Meanwhile, a Canadian/Soviet team cross-country skied across the pole using Warmlite® bags, which stayed dry and warm for the entire trip. Will Steger bought Fuzzy Stuff Vapor Barrier liners from Warmlite® for his bags for his much longer South Pole trip and, thus, kept his sleeping bags dry and warm his entire trip.”

a couple other related links

https://www.coolantarctica.com/Antarctica%20fact%20file/science/cold_acclimation_human.php

http://www.princeton.edu/~oa/winter/wintcamp.shtml#Personal%20Equipment

https://www.ukclimbing.com/articles/features/insulation_explained_part_1_staying_warm-5105

[Opogobalus]

I read skimmed through the warmlite stuff the other day. A couple of red flags in the science touted that need checking:

– Insensible fluid loss is the loss of pure water, it’s not the same as sweat which contains solutes. So yes you will be dehydrated by fluid loss, but it’s not as dehydrating as 4lbs of sweat which has those solutes (and is why we need electrolyte supplements in endurance sport activities).

– the 4lb of insensible fluid loss seemed a lot to me. A quick search couldn’t verify this number. Insensible fluid loss is typically estimated at 50mL/hr in unstressed hospital patients. In 8hrs sleep that’s 200ml. Roughly half of that loss is through respiration, and so shouldn’t be condensing in the sleeping bag (your shelter wall, however..)

Granted in proper cold weather I’m sure bodies behave differently. 10x as much fluid loss? Maybe my scepticism is misguided.

So further investigation needed on Warmlites claims, but the first-glance questionsbility and somewhat sensationalist tone of the article does not inspire confidence in the rest of their claims.

Yet I am quite convinced by the principle behind VBLs. I’m just trying to cut through the bs of that particular article (it’s almost as if it was written to sell a very niche product..!) and get a truer understanding. Thanks for the other links, will take a look when I get a moment.

[Jerry Adams]

yeah, I agree, that isn’t real scientific, more anecdotal, still, there are some ideas to consider.  Maybe it raises questions that should be studied more scientifically.

My anecdote is that the pair of pants I made from fuzzy stuff weighs 7.6 ounces.  I also made a shirt that’s somewhere else I know not where so I can’t weigh it but it weighs about the same.  In temps down to 20 or 25 F for 6 days they didn’t seem any better than a regular base layer that weighs about the same.  But the regular base layer (supplex) is better for general use, like when it’s warmer and I need bug and sun protection.  My wife said the fuzzy stuff, which is silver colored, looks like a Disco suit.

That was the end of the experiment for me because I don’t do longer colder trips.

[Opogobalus]

So good for discos on resupply days, another point in the VBL column.

My main interest in the theory is for times I am doing a hike with expected lows around the limits of my current sleep system.

If I can do a makeshift VBL with things I already have an get another 5c out of my system, then I’m less concerned about the potential for a cold snap, or camping in a less than ideal place (valley floor). I carry a rain jacket and windpants normally, but if I’m concerned about a 30f sleep system, I probably have rain pants instead of the windpants. I always have a packliner (feet and legs) and a couple of stuff sacks (hands). If i wear these things under my insulation layers, can i make that unexpected cold snap/poor site selection safe – or even better, comfortable?

If so, then the understanding Of how to implement it is good.

(I don’t think I’d plan or advocate using this system primarily, always try and pack with reasonable allowance for the expected conditions. But it’d be an “emergency” type piece of knowledge).

[Balagan]

@danepacker “Go to a military surplus store and buy the quilted liner for ponchos. Should be large enough and if too big then cut it down one side and re-sew.”

The PLUQ is made from a poncho liner. In tree hanger language, it stands for Poncho Liner Under Quilt. ;-)

[Edward John M]

200ml of insensible fluid loss in 8 hours sounds low to me so I think respiration loss needs to be added to that. 2 kilos sounds like an exageration tho  Personally I can vouch for a VB giving a decent boost to the temperature rating of a sleeping bag

[IVO K]

Jonatahn M’s “50mL/hr in unstressed hospital patients. In 8hrs sleep that’s 200ml” involves some fuzzy math.

50 mL x 8 hrs equals 400 mL.

[Opogobalus]

Some fuzzy reading perhaps? As stated, 50% of insensible fluid loss is respiratory – breathing. Which if you’re ventilating properly, should not going directly into your sleeping insulation.

[Hanz B]

In medicine we use a simple 421 to provide /  maintain hydration status of fluids if a patient isn’t drinking; you 4ml x the 1st 10 kg; 2ml x the 2nd 10ml and 1ml for all the rest of the persons kg. So you can imagine a 60kg person lying in a bed putting out low Mets would require a maintained rate of:

1-10th kg = 40 ml

10-20th kg = 20 ml

21-60th kg ~ 40 ml

thus total rate is 100ml/hr

In simple terms, we can multiply the fluid maintaince rate by a factor depending on further insensible losses: fever or hypothermia maybe 1.1x; add on infection maybe 1.2-1.3x. hence an patient may require 120-140 ml dealing with temperature instability or illness that requires the body to use up more fluids in ventilation and dehydrated.

Even so, a 60kg total 24 hour maintaince would be 2400 ml. Hence the 2L a day water philosophy assuming the rest or the fluids are in foods you eat.

I would hypothesize in a cold climate with a hard days work that the bodies losses are at least that of the above maintaince and would count on 800ml loss in a 8 hour night in a 60 kg person. Females slightly more.

[Edward John M]

So 400ml of water to remove from the warm layer each nite?

My experience so far has been minimal because it has been too warm to actually need the synthetic quilt over any of my down bags but so far my experience mirrors others who use this system. The weight penalty of the oversized overquilt isn’t that great compared to a summer weight synthetic quilt

[Author]

Posts