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RayBan
03-28-2011, 14:11
There've been a number of posts recently about sleeping bags not performing as rated and corresponding suggestions that it's not the bag but, instead, the sleeping pad that doesn’t have a sufficient R-value to prevent convection cooling, etc.

Some have suggested adding a thin CCF (closed cell foam) pad on top of whatever primary sleeping pad is being used to eliminate or lessen the cooling effect of otherwise low R-value pads.

Although relatively cheap, “thin” CCFs (e.g., from Gossamer Gear, Wal-Mart, etc.) are much more bulky in comparison to an effective alternative I created in an effort to stay as ultra light as possible without unnecessarily sacrificing functionality or incurring inordinate cost.

What I did was to start with a Thermo-lite Bivy 2.0 (pictured below and available for $26.50 from Amazon - http://www.amazon.com/Adventure-Medical-Kits-Thermal-Bivvy/dp/B000WY2962 (http://www.amazon.com/Adventure-Medical-Kits-Thermal-Bivvy/dp/B000WY2962) - and maybe cheaper elsewhere).

As you can see, the Bivy 2.0 is a semi-mummy shaped emergency “bag” with a foot box that vents.

The DIY process

1. I first put my mummy shaped sleeping pad on top of the flattened Bivy 2.0 and traced an outline of the Bivy around my sleeping pad. (I let the air out of my pad; I found that it doesn’t really matter much if the pad is “airless” or not).

2. Using an exacto knife, I next cut the Bivy 2.0 along the pattern I had traced. This left a 2-ply (i.e., folded in half) "mummy shaped" remainder (see pictures below).

PLEASE NOTE: I laid out the pattern in such a way that I cut off the vented foot box from the piece left.

3. After this, I cut the 2-ply remainder of the Bivy 2.0 in half (again using the exacto knife and cutting a very narrow strip where the two "sides" are folded to make one piece).

PLEASE NOTE: if you want to use a “sandwich” approach – i.e., with the pad in the middle and both modified Bivy 2.0 sides around it - then don’t make the cut I did.

4. After doing the above, what’s left are two separate pieces, both identically shaped and each having an "inside" (dull) and an "outside" (shiny) (see pictures below of each side and its appearance).

5. I next put one piece of this modified Bivy 2.0 on top of my mummy sleeping pad and the sleeping bag on top of it. (NB- In an effort to prevent the Bivy 2.0 material from moving around on the pad, I first "painted" the pad on top with Silnet "dots", which effectively "fastened" the cut Bivy 2.0 material to the pad. I also "dotted" the bottom of my sleeping pad and tent to prevent any similar "slippage" from movement/pitching on non-level ground. I could have "dotted" the Bivy 2.0 material but found it unnecessary to prevent "sliding".

End result: the "half" Bivy 2.0 mummy piece I cut/use weighs 56 grams (i.e, 2 oz.) and is comparatively MUCH lighter and VERY much more compact (about fist size) than any CCF I’m aware of. It also reflects back roughly 80-90% of the radiant heat that would otherwise be lost using a low R-value sleeping pad (such as my custom model) and prevents virtually all heat loss through convection cooling.

(For those wanting an even lighter approach, you can use a “space blanket” - i.e., aluminized Mylar. However, the Bivy 2.0 material is MUCH quieter.)

And no, I don’t make these/sell them/have a pattern for them. :sun

BrianLe
03-29-2011, 01:34
Thanks for sharing this. It would be interesting if there were some objective way of measuring the R-value improvement; perhaps if you posted at BPL some of the geekier folk there might have at least a decent estimate.

I think I'll stick with the thinlight ccf approach, in part because it adds a different sort of protection to my inflatable; I guess that I'm almost becoming superstitious or something, as on two long trails now I've had some sort of ccf pad under my inflatable and have yet to get even a pinhole leak.

Another factor for me is that I have a Neo-air inflatable, which "incorporates an R2 Barrier to reflect heat back to your body", i.e., I think the radiant heat thing is already covered for Neo air users. Just empirically, a thinlight on top of the Neo air makes a noticeable difference on colder nights.

To be clear, I'm not saying these things to undermine your good work or observations (!). For other pads this might be a great addition.

The Cleaner
03-29-2011, 08:09
What about condensation problems:eek:?...

garlic08
03-29-2011, 09:02
This is a good idea, and it has already been done: http://www.rei.com/product/804326

I do something similar for snow camping. I use a roll of Reflectlix duct insulation (free from truck stock). It not only adds a reflective layer, but also a little bit of R-value too. Very light, as well.

As I understand it, reading quickly, your addition goes below the bag so condensation is not a problem.

RayBan
03-30-2011, 09:41
This is a good idea, and it has already been done: http://www.rei.com/product/804326

I do something similar for snow camping. I use a roll of Reflectlix duct insulation (free from truck stock). It not only adds a reflective layer, but also a little bit of R-value too. Very light, as well.

As I understand it, reading quickly, your addition goes below the bag so condensation is not a problem.

Thanks for the link- I wasn't aware of the product but it/my DIY dovetail so it seems.

Several notes about my approach in light of the various comments made so far:

1. You can use the DIY with essentially any pad (like a Neoair with 2.5" height when inflated) whereas the product referenced (a) may not be as "comfortable" (at least for some), (b) is still more bulky than a deflated air-filled pad and (c) weighs more than simply using my combined sleeping pad/DIY approach, both of which attributes can prove to be significant factors where pack space/fit and base/aggregate weight are issues.

2. You can remove or re-position my DIY (from on top of the pad to the bottom of it) to control R-value and to eliminate possibly have to swap out pads on extended hikes (like the PCT or CDT) where you may run into substantially varying temperatures calling for a lesser R-value sleeping pad than in other areas/circumstances (e.g., southern section desert vs. hi-Sierra/Rockies portions of those trails).

BTW, I did post my DIY on the relevant backpackinglight.com forum for anyone to review/comment on. So far, no one seems to have taken exception to it on the basis of either effectiveness or potential condensation issues (the latter of which I've found from experience is a non-issue regardless of whether the "cut-down" Bivy 2.0 sheet is positioned on top or bottom of the sleeping pad).

enurdat1
03-30-2011, 10:13
At work, we actually use the same product, just a different name, to package patients when they are flown in the helicopter. They are great for thermal regulation, especially when it's cold out. I carry one in my day pack, and just thought about using one with my sleep stuff on a regular basis.