Mylar VBL failed

[chris markley]

My experiment with a mylar/space-blanket mummy-bag-shaped liner as a vapor barrier failed. The lousy $5 “emergency sleeping bag” mylar/space-blanket I bought from Amazon, shredded up in the middle of the night. Mylar is tough stuff, but mine ripped around the circumference a few inches down from the top opening, and also blew out at the taped side seam. Was I having a crazy dream and thrashing around? Dunno. Anyway, I was sleeping Friday and Saturday nights this weekend on top of a mountain in 10 degrees with a breeze, under a small tarp. I ended up being comfortable without the VBL and my second night slept toasty warm without it. My setup is to pull my Grand Trunk Nano 7 ultralight hammock through the zippered footbox of my Kelty Lightyear down 20 degree bag. When I get in the hammock, I reach down and pull the bag up over my legs and then zip it up so that I’m cocooned in the hammock with the bag zipped up all around me. Doing this in a hammock means the bottom of the sleeping bag isn’t compressed against the ground or against a sleeping pad, so you stay equally warm all around, top and bottom. The only downside is that the mummy bag’s narrow width does not let the hammock expand quite to its full width capacity, and you are slightly limited in getting the diagonal lay required to lay completely flat in a gathered-end hammock. Instead, you sleep with a slight curve in the hammock rather than flat, but I still find it amazingly comfortable. I slept toasty warm in 10 breezy degrees atop a mountain. I climbed into the hammock at 9 p.m. and didn’t get out until 7 a.m., well rested and refreshed. I wouldn’t have felt good sleeping on the ground in similar conditions, for sure. I can’t imagine ever sleeping on the ground again. Super comfortable. Super ultralight. Super warm. My entire sleep system, consisting of hammock, complete hammock suspension, tarp (MacCat Dexluxe in Spinnul, including ridgeline and guylines), tarp guyline stakes, and sleeping bag weighs 64.1 ounces (including various stuffsacks) and yields perfect, no-pain-in-the-back sleep and toasty warmth down to the 10 degrees I experienced this weekend, and probably lower (I was wearing smartwool longjohns and kept my down jacket on inside the bag, and had on a fleece beanie).

I’m considering a cuben fiber VBL. But since I was comfortable at 10 degrees with no VBL, and since I won’t often be sleeping in 10 degree cold (I hope), maybe it’s not worth it unless I’m out for a week and the bag gets heavier each night with sweat vapor. If I do splurge and buy a cuben VBL, I would wear the smartwool longjohns inside the VBL and drape my down jacket on top of me like a quilt, on top of the VBL but still inside the bag. I suppose that would be a good system.

Thoughts and comments?

[will sawyer]

Chris,
That is interesting that you were able to shred it…
I have been thinking of using emergency blankets as a cheap material to make a vbl quilt similar to the ones at enlightened equipment. Do you know what type/brand you were using? I'd love to hear more about that.

Also, great idea with the 'cocoon' around the hammock. maybe a montbell stretch bag would work even better?
did you leave the bag open a bit to breathe? did that create a draft/convection current inside? Or were you basically entirely sealed in, which would mean lots of breath condensation?

-Will

[Tohru Ohnuki]

Mylar 'space blankets' tend to be pretty worthless; they are noisy and shred very easily as you've found. You could make a liner from an AMK heatsheet which is polyethlene iirc. Or they make a emergency bivy bag..

[obx hiker]

I've had mylar emergency blankets to shred as well. Seems to be a property of the "space" blankets that a tear turns into a complete stem to stern rip.

OTOH The AMK bivy bag is tough and doesn't seem to tear if used with care..at least mine hasn't. I've used it as a vbl. Only problem is the poly or whatever added to the mylar is not really slippery and if you're a side sleeping toss and turner the bivy wants to turn with you and can get tangled up. You soon learn to grab the bivy almost in your sleep when you turn so it holds still. This might not be as big of a deal in a hammock since you could put the bivy around and outside the hammock but under the bag. Works great as a vbl.

What size are you? I have a grand trunk as well and your system sounds like a great idea.

[Dale Wambaugh]

Yeah, the AMK SOL Emergency Bivy bag is like their HeatSheets, with a polyethylene base. Should make a good VBL. They also have a thicker and heavier bag, called a SOL Thermal Bivy. They recently added "SOL" to the names, so you might see different stuff in stock. The "Emergency" model is 3.5oz/$16 and the "Thermal" version is more like 8oz/$32.

[Konrad .]

Pretty nifty setup…sounds like your turning a mummy bag into a topquilt/underquilt. I think im picturing it right…so the hammock goes in through the foot vent and out the hood? That means the hood is underneath the hammock right, so you don't have any head coverage? If that's not right, do you mind posting a pic of the setup? Thanks

[chris markley]

While you can't completely draw up the hood in this configuration, the hood material is behind your head, providing plenty of insulation. The rig appears in this video near the very beginning and then around 2/3 through. http://www.youtube.com/watch?v=4xUY6_uMGQY

[Richard Niemi]

The Adventure Medical Kits Lightweight (3.8 oz) Emergency Bivvy Heatsheets that Dale mentions are Great! Cost about $16. They are quiet, tear and puncture resistant, stretch a little and last a long time. Sharp items will puncture. I own a few. For winter use I sandwich my three season sleeping bag with two of these Spacebags. My sleeping bag stays dry. I sleep like I'm in a toaster and they are multi use. I sleep in a single layer of lightweight synthetic. I sleep on a heavier duty space blanket which I don't know the brand name. The idea is this reflects the heat back up to me and reflect to cold away from me. It is super puncture resistant.

Rick

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