Experimenting with a VBL

[AniOutdoor]

Last winter I tested stacking my Gemini quilts (http://leiavoia.net/pages/hammock/geminiquilt.html) with my 30*F quilts from Hammock Gear, and was able to sleep comfortably down into the single digits, or as cold as it got here.
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While this was nice and toasty for an overnight, and probably good down to 0*F with just a medium weight base layer on, it’s a bit too bulky and heavy for my 50L Osprey pack on a multi-day trip.
After deciding that the 30*F quilt set along with wearing my puffy jacket wouldnÂ’t cut it for temps down to 10*F, and a fleece liner like one from Sea 2 Summit wouldnÂ’t help reduce weight or bulk much, I figured I was gonna need to get a third set of dedicated winter quilts if I wanted to do any multi-day trips that dipped below 20*F.
It wasn’t until spring time, and temperatures were rising fast, that I came across Skurka’s article on vapor barriers (https://andrewskurka.com/vapor-barri...y-application/).
Before buying a 0*F quilt set, I decided to see if a VBL would work for me. I didn’t wanna invest the time and money into constructing something out of membrane SilPoly yet, so I decided to first try Mylar and tape.

The construction was simple, basically a giant top quilt I could fully wrap around myself, as well as a Mylar balaclava cut to go under my chin.
Photos from the project:https://imgur.com/a/QIFbH8d

The results we good, almost too good.
Even wearing just a lightweight poly base layer, loose knit wool socks, thin poly neck buff, and cheap stocking cap, I was hot pushing the 30*F quilt set down to a 15*f overnight low.
I say hot because I woke up and had to ventilate in the middle of the night.
I loosened up the neck cord quite a bit to allow some airflow between the quilt and Mylar.
When morning came, I was comfortable and dry from the knees up.
Below the knees didn’t get any ventilation and my socks and base were soaked with sweat.

I plan to test this Mylar system further, mostly for durability, and plan to reinforce some edges and corners with scotch tape.
My quilt has a hybrid foot box, and now I know next time to open that up to ventilate too.

[Salt]

Very cool. Those emergency blankets clearly do their job! I can't imagine the Mylar was overly comfortable though, right? I've been toying with the question of how many degrees further a silk sleeping bag liner would push things.

[AniOutdoor]

I used mylar because it was cheap and fast since it’s tapable.
It didn’t stick to me because I was still wearing my lightweight poly base layer, but it was rather loud to move in.
Silk would make an interesting liner to try out as well, but it needs to be a waterproof fabric to work as a VBL.
If the mylar doesn’t last more than a few nights, I will probably make one out of RBTR’s membrane SilPoly.
I don’t expect that to be quite as warm since it isn’t aluminized, but the durability will be worth the trade off I think.

[jakev383]

I have a double layer hammock and have been wanting to try a mylar blanket between the layers... It would probably make me sound like I was eating a bag of chips in my hammock though

[Vryce]

I am not an expert in this field by any stretch of the imagination. Yet I wonder if you were able to breathable heat reflective material, would still have the same level of comfort without the moisture issue? Food for thought.

[AniOutdoor]

According to Skurka, one of the main purposes of a VBL is to stop the transmission of perspiration away from your body and into your outer layers such as your down quilt.
This is important for multi-day winter trips where things cannot effectively dry out, but instead freeze.
Another purpose is to minimize evaporative heat loss, but in a way that’s kinda saying the same thing over.
My sweaty feet could have been prevented by me ventilating my quilt better. I have a hybrid foot box, not sewn closed, so I should have opened it up some and I likely wouldn’t have the same problem.
At least with the VBL that perspiration didn’t make its way into my quilt.

[cmoulder]

Good discussion HERE.

Starting around post #134 I began my testing with Lightheart Gear rain suit which turns out to be a very good VBL because unlike just about all other rain gear it is truly non-breathable.

VBL is a very good tool for multi-night trips in extreme cold where frozen condensation collects inside the quilt and can't be dried out, which renders the quilt very ineffective as an insulator after only 2-3 nights. And it gets worse from there — if you cannot somehow externally warm up the quilt and get rid of that ice you could be in serious trouble.

[joe_guilbeau]

There is supposed to be a 10-hour hand warmer that you can use for the feet. I don't recall the manufacturer.

[tlfillingim]

The Hot Hands hand warmers claim 10 hours. My experience say it's probably more like 6 hours of adequate warmth.

https://smile.amazon.com/HotHands-Ha...%2C1318&sr=8-7

[BillyBob58]

Aha! VBs rear their controversial heads once gain! I have not commented on VBs in a long time, about a year I think! But since I have previously written endless pages on that subject, then it is probably well appreciated that I have not.

According to Skurka, one of the main purposes of a VBL is to stop the transmission of perspiration away from your body and into your outer layers such as your down quilt.
This is important for multi-day winter trips where things cannot effectively dry out, but instead freeze.
Another purpose is to minimize evaporative heat loss, but in a way that’s kinda saying the same thing over.
My sweaty feet could have been prevented by me ventilating my quilt better. I have a hybrid foot box, not sewn closed, so I should have opened it up some and I likely wouldn’t have the same problem.
At least with the VBL that perspiration didn’t make its way into my quilt.

There Ya go, you are realizing one of the main most benefits, especially for longer trips(more than a night or 2) I always say/ask: "True, even though condensation on a WARM VB is very unlikely, you can always overheat and sweat. Especially if not venting adequately. But would you rather have condensation and/or sweat accumulating in your quilts, or held close to your skin, thus keeping your insulation bone dry night after night?

And the warmth added is two fold: the above mentioned drier insulation, PLUS the blocking of evaporative cooling(think swamp coolers and air conditioners), which by itself can add about 23ºF of warmth.

I prefer VB clothing, especially from Stephenson's Warmlight(sp?) with Fuzzy Stuff lining directly against my skin. Very comfy and relatively inexpensive!(or used to be at least)

I last used VB clothing almost a year ago on a Christmas trip to the NC mountains, sleeping at about 3000 ft. I was using a 30F rated SG insulated hammock, with a 30F rated SMR Inferno TQ. The forecast lows were 18-24(depending on which weather station) plus at least 3 MPH of wind. I did not pitch my tarp, as I was on an elevated porch, but I was concerned with wind. So, I layered up. I had not brought my VB clothing. So I faked it by wearing my UL breathable rain top and pants over my COTTON PJs. (I know, that- WPB rain gear- should not work as a VB, but it actually seems to do a pretty good job). Over this faux VB clothing, I layered my very light puffy synthetic jacket and pants( a 12 oz jacket and 8 oz pair of pants). No VB socks this time, just the thin nylon socks I had worn all day. I wrapped a light weight puffy down jacket around the hammocks foot end, and a thin AHE CCF pad in the footbox of my TQ.

By the time I bailed at 0200 or 0300(noisy farm animals kept waking me up, particularly a noisy donkey), it was 25F + wind chill, and my main problem had been from over heating. It didn't take long to pull that pad out from under my feet and lower my hood. And I was still plenty warm, except for cold ears. I have little doubt that most of this excess warmth was due to the fake VBs (breathable rain gear) I had been wearing. I'm confident I could have been warm enough AT LEAST 10º colder( or to 15F), or maybe even a good bit colder. All with 30F rated quilts and light layering, rain gear put to double duty as VB, and no tarp to block the light wind. For me, this was just one more testament to the efficiency of a VB approach.

Good discussion HERE.

Starting around post #134 I began my testing with Lightheart Gear rain suit which turns out to be a very good VBL because unlike just about all other rain gear it is truly non-breathable.

VBL is a very good tool for multi-night trips in extreme cold where frozen condensation collects inside the quilt and can't be dried out, which renders the quilt very ineffective as an insulator after only 2-3 nights. And it gets worse from there — if you cannot somehow externally warm up the quilt and get rid of that ice you could be in serious trouble.

Yep, post #134! We have had some lengthy previous discussions on this subject, no?