Waterproof Quilt – 2 Options…

[Nicolas]

I will use the second post for my entry because it’s not possible to edit the original post with this forum…

[Nicolas]

This is a myog project but it is in a relatively early design phase so the feedback I am looking for is not that myog specific.

I am thinking about a waterproof (wp) 2 season quilt with:
* 175g of down
* baffles = not sewn through
* velcro or omni tape on the sides in order to attach it to the bottom of the sleeping pad (sleeping pad has velcro/omni tape on it’s bottom as well).

Reasons for a wp quilt:
* no loss of loft due to wet down
* no damage to down when stuffing it in case down is wet/damp and in case it is not possible to dry it
* no need for drying time in case sleeping bag is wet / damp
* less added weight due to water absorption. I find it hard to quantify that difference. Did anyone weight a sleeping bag in the evening and then again in the subsequent morning? The silk sheet I have between me and the wp material would also absorb water (my sweat) but it would dry much quicker. And the wp quilt solution would of course also absorb some water but it would be very minimal especially with the silpoly fabric (instead of nylon).
* shelter can be more minimalistic
* all of these are the more important the longer the trip (without extensive breaks in hotels / at home etc), the wetter the conditions, the more minimalistic the shelter.
* Not an advantage compared to normal quilts but an advantage compared to normal vbl bags: Overheating is no problem because you can always vent the wp quilt like a normal quilt which is possible but a little bit more cumbersome with a normal vbl bag.

Downsides of a wp quilt:
* between ~65g to 178g higher “dry weight” because there are lighter non waterproof nylon fabrics (0.66 oz/yd² = 22,4g, 10d nylon) compared to the lightest waterproof (non dyneema) fabric (0.93 oz/yd² = 31,5g, silpoly membrane) and because there is some seam sealing needed if one wants to make it really waterproof plus a tiny bit of additional fabric or velcro (see options below) is also required.
* Reduced sleep quality due to dampness: I am not sure yet how bad this really is. I have personally slept in traditional vbl bags and the effect of the dampness on my slep quality was not dramatic. I would always have a silk sheet between me and the wp fabric which I would bring anyway for hot days. Nevertheless dampness might be an issue – something I have to test in practice.

 

I have two options (as far as I can see):

Option 1) Make a “normal” quilt (rectangular, no sewn in foot box) with breathable nylon top and bottom fabic plus a waterproof bag (made of silpoly membrane, shaped like the quilt) which is open only on the head end in order to insert the quilt. There is a velcro closure on that head end. If I want the quilt to be waterproof, I put the quilt into the waterproof bag. To keep the quilt in place within the wp bag I use velcro which is sewn to the inside of the wp bag (the quilt has velcro on its sides anyway).

Option 2) Make a quilt with a waterproof top and bottom fabric (silpoly membrane). The top and the bottom fabric is sewn together only at the top end (where your head is). In order to allow the quilt to loft and pack down, the top and the bottom fabric on the sides and on the foot end are held together through a nylon strip which is downproof and breathable.

Advantages of Option 1)
* more waterproof which is relevant when the shelter gets more minimalistic
* in case a waterproof quilt turns out to be a stupid idea, I can still use the quilt as a normal quilt and the wp bag as a normal vbl bag.
* I might not need the wp bag on some nights in dry environment and when I have lot’s of time to dry things the next morning -> eliminate effect of dampness on sleep quality on those nights.
* lofts and packs faster
* allows for “head hole” to use the quilt as a parka and to attract other weirdos (example: http://www.jacksrbetter.com/wp-content/uploads/2012/05/Wearing-Stealth-web-sm.jpg)
* dries quicker if needed
* absorbs less water because it’s completely sealed. My guess is that the differnce would be minor (~ 10g).
* dual use for wp bag as standalone bivy bag (but then not with a down quilt/sleeping bag)

Advantages of Option 2)
* ~102g lighter: (weight of wp bag) – ((weight of option 2 fabric) – (weight of option 1 fabric)) = (5m² * 31,5g/m² = 157,5g) * ((5*31,5g = 157,5g) – (5*22,38 = 111,9g)) = 157,5g – (157,5g-111,9g) = 157,5g – 45,6g = 111,9g. Minus 10g because of less water absorptoin in case of option 1 -> 101,9g The additional weights for both options (additional seam sealing, velcro etc) cancel each other out (I made a rough calculation).
* ~ 40 USD cheaper because I would need less fabric.

Did I miss any advantages or disadvantages?

[Lorenzo M]

I’d go a maximum of one side, outer obviously wp otherwise it’ll loft by morning. Rsbtr recommend that for robic 7d and they are spot on.

[Mark Fowler]

A couple of comments:

vbl systems work best at temperatures below freezing – not 2 season type temps.

If you make a waterproof quilt (option 2) then you need to leave sections that are air permeable to allow the quilt to loft and to expel air when packing it up.

Water resistant down removes to a reasonable degree issues with down getting wet.  Truly wet sleeping gear is a product of either carelessness or calamity.

[Nicolas]

Btw, is it not possible to quote a passage from one of your messages?

@enzo said: “I’d go a maximum of one side, outer obviously wp otherwise it’ll loft by morning”.
That is a no go in my view because all of my sweat would accumulate in the quilt since it can transpire into the quilt but not out again at the top.

As for lofting: The reports about lofting from the following waterproof quilt projects suggest a lofting time of minutes rather than hours or days: https://backpackinglight.com/forums/topic/10oz-cuben-fiber-quilt/#post-3446793 https://backpackinglight.com/forums/topic/10oz-cuben-fiber-quilt/#post-3446745. Also note that Peter’s @nash-pcomcast-net breathable patches have less surface area than the breathable surface area in my case would, so lofting time should be ok.

Also the research done here https://backpackinglight.com/forums/topic/12505/page/2/#post-1427673 suggests that maximum loft isn’t necessary to reach maximum warmth of a given amount of down fill. But I have do read more about that still, this is just what I grasped at the first glance so I might be wrong here.

@kramrelwof I will reply later with a drawing to illustrate the air permeable sections I would sew with option 2. I have described those in my original post (in the paragraph about option 2) but maybe that wasn’t clear enough.

[Lorenzo M]

From my experience a small patch of downproof breathable material for lofting is inadequate. But I don’t hang around in camp so YMMV. A wpb outer would be the way to go IMHO, the 7d robic is my choice, not quite wp, hh is over 1000mm and 7000 breathable but 0.7oz/y.

If you go wp both sides with air permeable patch I’d worry if moisture got to it, it would be impossible to dry on trail. Any of the 10d fabrics m10, Dutches stuff etc will allow down to dry very quickly in the sun in my experience.

[Matt Dirksen]

Out of curiosity, what kinds of trips are you planning to use the fully wp quilt on?

(And part of my reason for asking this is because I am having a difficult time understanding when a wp quilt would provide an distinct advantage over some material to the contrary, or with an insulation that can effectively manage both water and vapor transmission.)

Thanks,

Matt

P.S. I wonder if you might reach directly out to Tim from Enlightened Equipment for some pointers, Since he’s essentially “been there/done that”. He may provide some good insight and answer your questions in a Good Way.

[Douglas S]

I think a fully wp quilt would be helpful at any time the dew point is within or on the surface of your quilt to minimize condensation within or on the surface your quilt from your own transpired moisture.

[Nicolas]

Applicability: I have done a 7 day long trip in Patagonia (almost constant rain, 10° C). The condensation that formed on the inside of the tent’s fly was dripping down on my quilt. The quilt lost more and more of it’s loft over the days. I had to stuff the quilt wet and couldn’t dry it for several days. This is of course the least ideal condition for a (non wp) down quilt. But even in less extreme conditions I often have dew on the surface of my quilt in the morning. And if you want to use a very minimalist shelter spray protection is required. I don’t fully trust a DWR coating to keep the down completely dry. The only real solution is a waterproof top fabric (or the solution I discussed as “option 1”). And if you make the top waterproof the bottom has to be waterproof as well otherwise all the perspiration ends up in the down insulation.

A wpb top (and bottom) fabric? The breathability of wpb fabric does not provide any advantage as far as I can see: A wpb fabric would only make sense if it was used ONLY for the top fabric because you don’t need any breathability if the the bottom fabric is wp.* If you make the bottom out of a breathable fabric (a uncoated nylon or a wpb fabric) then breathability at the top fabric matters but in that case I would rather go with a DWR treated Nylon since the breathability of a wpb fabric will not be enough to avoid condensation. These are just unscientific guesses. My guess that a wpb top fabric will not be sufficient to avoid condensation is a.o. inputs based on this piece https://40yearsofwalking.wordpress.com/2011/07/04/the-bivy-condensation-conundrum/ in which the author shows that even uncoated nylon fabrics regularly result in condensation. I don’t see a reason why there should be a significant difference between condensation on the inside of a bivy bag (with a breathable top) and the top fabric of a sleeping bag in terms of condensation.

* There might be a case in which a wpb top fabric would make sense: If you have condensation inside the quilt not from your perspiration but merely because outside temperature cools off quickly enough during the night so that the warmer air inside the quilt condensates on the inside of the now cooler top fabric of the quilt. In that case a breathable top fabric might help. But I do not know enough to be able to judge weather the water vapor permeability of a wpb fabric such as the one mentioned by Lorenzo would be sufficient to avoid condensation in this case. Hmmm :) Anyway this is another argument for option 1 since drying is easier in this case.

Indeed it would help a great deal if @marshlaw303 could share his thoughts whether I am completely off track here.

@enzo do you have a link to that 0.7 oz/yd robic fabric?

[Matt Dirksen]

Thank you for your clarification, Nicolas.

Based on your experience of tending to a wet quilt in 10d rainy weather, I can understand your desire to create a fully waterproof quilt.

My concern is the following: 1) based on what you described, (100% rain, 10d), the ambient humidity in your tent was likely in excess of 90%. At that saturation level, condensation will pretty much occur on everything (especially from your breathing.) 9.5d is the dew point at  95% humidity 2) While a wp quilt interior will prevent  your body’s vapor from passing through, any air that was used to “loft” the quilt will be subject to the same relative humidity you are residing in. Therefore, you quilt would still be at-risk for interior condensation. With an outside WP membrane, the vapor would likely condense on the inside of the surface of the outer layer.

3) In the Bivy Condensation Conundrum article you referenced, remember that the author’s greatest success was with his first bivy – with a breathable top.

For many years, I used an Integral Designs bivy (same material as Bibler’s Todd Tex). I never had any uncomfortable condensation issues, and I used it in all possible manefestations of nasty weather. I believe the reason why it worked so well was due to the materials ability to manage condensing vapor. (It has a fuzzy interior film, which was very “hypophillic”, if I recall.) I also tended to toss some clothing in-between my bag and the bivy to create “air pockets”. This helped a lot.

Nowadays, I have found that using a very breathable “downTek” quilt to work extraordinarily well in wet environments. But in particular, when I am concerned about sleeping at or near the dew point, I have used a very light silk liner over top of my quilt. This has helped mitigate any condensing vapor as well as water dripping from the ceiling of my tarp. It also adds about 5d to my system.

As a general rule, I have found that creating ways to “dry off” to be just as important to safety and comfort as trying to not get wet. Folks tend to only think about “not getting wet” as the solution, but I offer that “properly mitigating the condensation that will occur” to be just as essential. The silk liner (or even perhaps a light pack towel over a quilt) could go a long way toward migrating any condensing vapor.

Best,

Matt

 

 

 

[Edward John M]

Wasn’t somebody making quilts using glued baffles and UL Cuben a while back? Made the bottom section from a very open material so it could be stuffed etc.

 

[Nicolas]

Matt,

thanks for sharing your experience and the hint with the silk liner. I think I will try that as well.

Can you clarify what the “d” refers to that you used in “10d” and “9.5d”? C (celcius) would have made sense to me in these contexts :)

You said: “…any air that was used to “loft” the quilt will be subject to the same relative humidity you are residing in. Therefore, you quilt would still be at-risk for interior condensation. ” As far as I understand the condensation process, the air that was used to loft the quilt is only at risk of condensation IF the temperature drops (enough) after having lofted the quilt, making the top fabric of the quilt cold enough for condensation to form. In any case, your are right, condensation can form without the influence of sweat.

It would be interesting to find out how much moisture is dumped when the temperature drops, say 20°C (e.g. from 25° to 5°) and compare that to the amount of perspiration per night (I have read that it is between 200 and 500 ml per night but the sources are not that super reliable: https://www.washingtoncitypaper.com/columns/straight-dope/article/13040026/straight-dope-do-you-really-sweat-one-liter-each-night, https://www.dr-gumpert.de/html/nachtschweiss.html, https://www.quora.com/How-many-grams-are-in-1-liter). Maybe the effect of condensation due to the temperature dropping is insignificant and can be ignored?

(source: https://de.wikipedia.org/wiki/Luftfeuchtigkeit = German wikipedia entry for “humidity”; I couldn’t find an English equivalent; x: temperature, y: amount of water in gram per m³ at a certain relative humidity level)

Let’s say we loft the quilt at 80% relative humidity and 25°C (acc. to the graph above that equals 20g/m³). Then the temperature drops to 5°C. For condensation to occur relative humidity would have to rise to 100%. 100% relative humidity at 5°C can hold 12 g/m³. 20-12 = 8 g/m³ will have to condense. Estimate of the volume of the quilt: 2m*1,25m*0,038m = 0,095m³. Finally: 0,095m³ * 8 g/m³ = 0,76g of water = 0,76 ml will be the maximum amount that will condense under these conditions. In reality even less will condense because my body keeps parts of the air in the quilt warm so the temperature drop does not occur for the entire volume of the quilt.

If the above calculation is right then 0,76 ml of condensation due to ambient temperature drop is insignificant compared to the 200-500 ml of perspiration per night.

The conclusion would be that 1) sealing of the bottom of the quilt (= a waterproof bottom quilt fabric) would make sense (to prevent condensation due to perspiration) and 2) the top fabric does not have to be breathable if the bottom fabric is waterproof.

Any flaw in my calculations / assumptions?

[Link .]

Tim at Enlightened Equipment made Cuben Quilts for a while starting about 9 years ago CUBEN / DOWN QUILT . and BPL member Peter Nash has made some 10OZ CUBEN FIBER QUILT .

[Matt Dirksen]

Hi Nicolas,

Thanks for sharing your thoughts (and calculations) about how much condensation you may get inside the quilt. While I honestly would need more time (and less mundane distractions) to look into your calcs so see if I can better understand them, I have a couple of thoughts:

1) While I believe your calcs may represent the amount of vapor potential from the air inside the quilt baffles at the time you begin sleeping, remember that the air must be entirely sealed off (like an air mattress) for this to remain the same throughout the night. I believe the general issue is if the outer layer is waterproof and you have restricted air to move freely through various air holes, then any saturated air exchange will still continue to occur during the night. This process will occur through simple convection (since vapor is transported much more effectively though the air than through a material.) And once any trace amount of vapor condenses, the water molecules will behave very differently in an absorbed state then they would in a gas or liquid state.

2) Sleeping in humid, soupy weather is not very comfortable – at all. All the moisture from your respiration as well as any moisture from your body will still exchange with the air in your shelter (as you toss & turn) continuously “adding water” to the air. Finally, if you are sleeping in constant rain, than the air surrounding your shelter is already saturated, so venting wont help much unless it’s windy, which could provide a tiny amount of drying potential. But this is why folks sleeping under a tarp in the rain can still wake up with everything under the tarp covered in condensation. It’s not just about the condensed water dropping from the underside of the tarp, but from water molecules in the air itself finding nice quite places to stick to. (I will insert here that I believe the silk liner over top of my quilt system really helps in this situation – it’s like one very large but thin sponge. To a vapor molecule, it’s got a lot of places to settle into and spread out into, thus reducing the risk of condensation.)

3) Something to pay attention to is how absorbed water molecules behave. Once vapor molecules begin the process of “absorption” on a surface of a material, they tend to attract even more vapor molecules. Here’s a link to a good piece on the absorptive state of water. This piece reinforces why the silk liner works, by reducing the concentrated build up of water molecules – which ultimately turn to condensation.

Finally, When it comes to untreated down, it takes a very little amount of water to impact it’s loft. My suspicion is that if the outside is waterproof as well as the inside, and the air is not sealed off, then any trace amount of water inside would be next to impossible to dry out. A permeable outer layer would make it much easier to dry out, even though it “might” get wet only once in a while.

So to answer your original question, I’d bet having a permeable outer layer would be a better bet, simply to allow your system some drying potential if it does get wet – unless you plan to completely seal off the quilt from the outside air (like a semi-inflated Neo Rest, or something). Regardless (as others have said), the general consensus is vapor barriers are very uncomfortable to sleep under in temperatures above freezing. Even under freezing, they may never really be considered “comfortable”, but more of a necessity on extended travel in freezing / wet conditions.

I believe those of us trying to hike as lightly as possible will always examine ways to reduce weight, even if it means sacrificing comfort. But on an extended trip in “cool” (but not cold) weather where one is subjected to saturated air the whole time, I would personally examine means/methods to “dry out” first and foremost before I would consider a vbl system or a completely waterproof quilt.

Best,

Matt

[Jerry Adams]

If you have any waterproof fabric on the top, you’ll get condensation.  Even if you have breathable areas or strips.

M50 fabric has a good DWR.  It’s waterproof as long as rain drops aren’t falling on it.  No condensation (as long as you’re not breathing into you quilt.  While you’re sleeping, body heat results in water vapor passing through the M50.  I’m sure RSBTR has similar fabric.  In my experience.  I sleep with no shelter about half the time.  Dew, mist, rain splash from when I have a tarp.

I’ve made a couple down quilts and vests with asymetric sewn through baffles:

That’s just a rectangular piece which was a test.  The ease of sewn through construction.  The benefit of baffles.  I don’t think I’ve convinced many people about this though : )

For 2 inch baffle, make the inner fabric baffles 3.125 inches wide.  The loft of the finished quilt will be 1.25 inches.  Or scale everything up.  You also have to make the inner fabric baffles 1.125 inches wider in length on each side.

[Terry Sparks]

Wouldn’t it be far better, easier,cheaper and probably warmer to wear a vapor barrier (rain gear comes to mind) as part of your sleep wear? I’d be inclined to use a thin synthetic quilt over the down bag/quilt to keep condensation from wetting the down bag.

[Lorenzo M]

10 days of rain at 10 degrees C is pretty standard 6 months of the year in the UK.  Frankly in those conditions your better off with an Apex bag.

[Nicolas]

@namelessway  regarding 1) why would it matter if air could be exchanged throughout the night? The air during the night is colder and therefore holds less water (normally) than the air inside the bag. Air exchange therefore would be a good thing (all other things being equal).

@retiredjerry “If you have any waterproof fabric on the top, you’ll get condensation. Even if you have breathable areas or strips.”… Have you read my complete OP?

@firebug If the down quilt is the only thing you want to protect from getting wet wrapping the two options I presented are the lightest options. A vbl bag is heavier or has the same weight as option 1 if you make it small but than it’s a lot less comfortable and you can’t vent it easily. Rain gear isn’t fully water vapor proof and because of the fabric used and because there are gaps between the top and the bottom and between your wp socks and the bottom…. A synthetic quilt is a catastrophe in terms of warmth to weight but would solve the problem of course.
Thanks everyone for all your comments. I will proceed with option 1. I will put the waterproof bag described as option 1 to the test as well as the silk liner mentioned by @namelessway. I’m already curious about the results :)

[R]

EE Revelation Apex vs 850 down at this temp are only 0.8 ounces apart and this use case is a ringer for synthetic’s ability to insulate when wet and dry far quicker than down. No baffles means no needle holes means DWR will be a lot more effective. You could also customize with a wpb upper layer.  Not needing to seam seal baffle stitches will balance the weight deference of down vs synthetic.

I assume you’ve got some sort of ground cloth. Trading that for a light (5oz) splash bivy to manage the drips instead of tasking the quilt with that job is another viable option and you get some additional warmth for the added weight.

[Author]

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