Does anyone use a Thermo-Lite® Bivy Sack instead of sleeping bad to save weight?

[refreeman]

Does anyone use a Thermo-Lite® Bivy Sack instead of sleeping bad to save weight?

Well www.steapandcheap.com (http://www.steapandcheap.com/) has a Adventure Medical Thermo-Lite Outdoor Bivy Sack 1 person for sale for only $15.00. I was thinking that it may be the best ultra lite way to hike and save weight. Another site says the weight is 6.5 ounces and has dimensions of Size: 36 in X 84 in.
http://www.adventuremedicalkits.com/products/KIT_e_ess_onebivvy.htm (http://www.adventuremedicalkits.com/products/KIT_e_ess_onebivvy.htm)

The Thermo-Lite Outdoor Bivy Sack for one person from Adventure Medical Kits provides protection from an unexpected night out. The durable Thermo-Lite fabric reflects and retains up to 80% of radiated body heat. Thermo-Lite offers higher performance for extended use than conventional reflective materials and provides superior handling in high wind situations. The survival experts at Adventure Medical designed their Bivy Bag to withstand repeated use, whether in emergencies or as a sleeping bag for fastpacking. The Thermo-Lite Emergency Bivy now comes with a reusable, lightweight stuff sack.

The Regular price is $30. I checked some other sites and $15 at SAC seems to be a real price cut.

So, what does anyone think this is a good idea and or a good deal?

How much does an ultra-lite sleeping bad usually weigh?

Thanks,
refreeman

[virtualfrog]

It's cheap, aye. But, it has little insulating value, and condensation can be a bitch.

There is a sleeping bag design out there though that's basically a fleece zip up bag wrapped in one of those. The guy says he's good til about 30 degrees or so. Wish I could remember his name...maybe somebody can help me out here?

[fiddlehead]

I slept in a bivy once. In the rain! it sucked. i prefer my 14 oz sil-shelter in which i can cook, read, wait out a rainstorm or snowstorm and be comfortable. A bivy is too much like a coffin to me.
It might be a better idea on the PCT where it doesn't rain much until you hit OR/WA. But a garbage bag might work there too. Yeah $15. is cheap for sure. But maybe you might want to try sleeping in one a few times before taking it out on the trail. just my 2 cents!

[wentworth]

http://www.thelightweightbackpacker.com/makegear.html
click on the link "Falk sleepingbag"

[Frolicking Dinosaurs]

I've slept in something very similar to the Falk bag (http://www.thelightweightbackpacker.com/makegear/falk-sleepbag/index.html) in an emergency many years ago and it was surprisingly warm for the weight. However, it would not have lasted more than a week to ten days IMO and it is very loud when you move around. Also, the lining had to be removed and allowed to dry after use.

[jaywalke]

I carry one of those for search and rescue as part of my beefed-up ten essentials, and once a year we bivy with just what we carry in our ready packs. We usually do it in the fall, on a night near freezing.

I survive (which is the whole point), but I don't exactly sleep. It's noisier, sweatier and at the same time not as warm as a sleeping bag.

I can't speak for you, but I'd be miserable on a thru-hike with one of those.

[refreeman]

Thanks everyone I decided not to get the Bivvy. (I was very close to buying it) Everyone’s points about condensation, noise, comfort and durability rang true to me, so I'll buy an ultra-lite sleeping bag...

Now I’ve got to choose one J
Any favorites you’d like to recommend?

[SGT Rock]

Jacks are better quilts.

[DLFrost]

Does anyone use a Thermo-Lite® Bivy Sack instead of sleeping bad to save weight?
I use one during the high heat of summer in place of a sleeping bag--it weighs half of what the down bag does and works fine. (This is with the ultralight setup carried in a daypack.) As soon as it gets at all cool I take a WM Ultralite, upgrading only during the colder parts of winter.

I selected the Adventure Medical product because the polyester fabric is quiet and because I'm one of those people who don't sleep well without a blanket or bag of some sort. For persons interested note that the velcro operning runs 2/3s the length of the sack.

Doug Frost

[ScottP]

I used one for a small section of my thru-hike during June/July in vermont along with a sleeping bag liner. It was pretty miserable. I learned that it wwould only keep me warm for half the night, at which point there would be so much condensation that I got cold. I ended up sleeping with just the liner for as long as I could before climbing into the bivy. Even in the summer in new england, I don't think that one of these is enough to sleep comfortably.

[Vi+]

Frolicking Dinosaurs,

You provided a link (Post #5): http://www.thelightweightbackpacker.com/makegear/falk-sleepbag/index.html

I believe the site misunderstands the Vapor Barrier Effect (VBE), which is based upon our perspiring. (Warning: I don’t understand the VBE fully.)

When our perspiration evaporates we cool (evaporative cooling). This occurs because perspiration is allowed to leave the surface of the skin.

When our perspiration doesn’t evaporate the body stops perspiring and we feel warm (the VBE). We can cause this by placing a water vapor impermeable layer very close to our skin. As the humidity above our skin comes close to 100% we cease perspiring and feel warmer.

The site's caution - “Over dressing may cause you to sweat, which can not vaporize through the foil, making you cold.” - is key to a problem. Perspiration has been allowed to evaporate into the clothing within the bag - evaporative cooling - making you cold, and water has condensed inside the clothes above the skin creating a heat sink, making you colder still.

This is an interesting mental conflict, that evaporating and non-evaporating perspiration has opposite effects.

Your understanding and acceptance of the Vapor Barrier Effect theory become challenged when you’re standing there, already cold, with your clothes still on, contemplating removing your clothes before crawling into a freezing piece of foil. For maximum effect, you need to remove all your clothes before you crawl inside the bag.

The Vapor Barrier Effect makes us feel warmer by as much as 22 degrees Fahrenheit. When you consider nighttime mountain temperatures, 22 degrees isn’t going to make you feel toasty very often. I carry two bags. One bag for the VBE. The other bag to be used outside the first. Clothes padded beneath the inner bag function as a “ground pad.” Filling the space between the two bags with leaves and other natural detritus operates as “sleeping bag fill.”

[GlazeDog]

I used a silk bag liner this summer in Allegheny Nat'l Forest. I used a poncho made from breathable/waterproof fabric as blanket at night and raingear at day. Plenty warm with my normal summer clothing. Definitely a one season setup though.

GlazeDog

[GlazeDog]

p.s. silk bag liner 3.8 oz. from sea to summit

GlazeDog