Underquilt vs Padding

[blackbishop351]

One problem - it still isn't hard measured data - again it is simply anecdotal evidence - somebody's experience. We have that - for and against.

I'm all for laboratory testing, but unfortunately most of use don't have access to the types of equipment and facilities necessary. That's actually a common problem for me - I'm in a Physics department at a liberal-arts-oriented school. We don't have a graduate program, either. Hence, no money and no nice lab facilities. So - also partly due to my own innate tendencies - I'm primarily a theorist. The theory/experiment divide is what I'm seeing between our opinions.

I have theory on my side of the space blanket discussion. Check any intro physics or undergrad Thermal text. Radiative heat transfer is minimal at human-environment temps, especially compared with convection. Fortunately, I also have experiment on my side - as I'm sure you know, physical theory isn't considered "reasonable fact" until it's borne out by experiment.

I'm glad you make the distinction here between laboratory testing and personal experimentation. Until someone takes enough of an interest to devote some serious, controlled, objective lab time to testing a variety of insulations and conditions, there won't be what I consider hard evidence. Until then, we have to rely on the opinions and experiences of others. And when it REALLY comes down to it, we can't rely on anyone's experiences but our own.

I'll be sure to post my OPINIONS on the SS as soon as I get some testing time in.

[blackbishop351]

Just an off-the-cuff thought here, but it appears from the Hennessy site that at the time Tom released the SS, JRB was already selling their quilts. Hennessy would've been deficient by not selling some sort of insulation, so I wonder if Tom came up with the SS simply because the Jacks beat him to the quilt?

[Just Jeff]

I thought I still had my thermo book but apparently I threw it away after that hideous class. But somehow I kept my astro book (must not have been buying this one back that semester ). So here are a few quotes about radiative heat transfer...

"With your eyes closed on a summer day, you can feel the Sun's heat beating down on you. But light and heat are only a part of the Sun's electromatic radiation..." (61). So we feel radiative heat transfer from the sun to our bodies in normal temps.

"Radiation or radiative heat transfer...involves the transfer of energy from one point to another through electromagnetic waves. If you've ever held your hand in front of a glowing space heater, you've felt radiative heat transfer" (322). So it also happens at temps that would heat up a room. And the new smooth-to stoves heat the pans through radiation since the heating element doesn't actually touch pan, right? Higher temps than a hammocker experiences but still not cosmic.

One more example. When my kids get a high fever, I can hold my hand near their heads and feel the heat coming off. Heat is being transfered from their bodies to the environment, and then to my hand. That's radiation/absorption at normal living temps. (Well, a few degrees above normal, but still.)

As an afterthought, why is a radiator in a car called a radiator - it doesn't really radiate much heat away from the engine. It provides a larger surface area so convection can remove the heat as you drive. Odd.

[slowhike]

if any one's interested in a newer, quieter version of the space blanket, BPL.com has a one person & a one-two person version available now.
they say this new type of space blanket is more durable & easier to refold than the old stuff too.
BTW... i have no connection to BPL.com... just find a lot of interesting stuff there<g>. ...tim

[BillyBob58]

TeeDee By making the GG crosswise pad 39", I also get shoulder insulation. It would be interesting to find Tom's source, or any source, for that OCF he uses. The OCF would definitely pack into a smaller volume. Not too sure about the weight, those 3/8" GG pads are really light. Buying the 40" wide 1/4" GG pad and trimming would also work and give you one GG pad instead of two. My concern would be rolling that 40" wide pad into something packable. With the 2 pads, I just lay one on top of the other and roll.

What does that long OCF pad weigh? I think mine for the explorer is about 7 or 8 oz. I wonder what the r-value is when not compressed? The torso/kidney booster seems is about 2 or 3oz. All will compress down very small. Though I have often thought of getting another full length ocf pad or more torso/kidney pads for temps below the teens. I'm sure it would work, and it would be light and small. BUT, no good on the ground and less secure against water, though better than down, I suppose. So I will probably stick with some combo of ocf/ccf. Those GG thinlight( is that what you use?) pads seem to run about 5 Oz for the 3/8", r-value 1.42. That really is light! The web site says they are not meant for padding, but for insulation? Are they trying to tell us they wouldn't be good for the ground? Do you feel that yours would work on the ground as well as regular ccf, or do they compress more under your wt? The Nightlight 3/4" weighs 8 oz., and has an r-value of 2.2. Thats about the same as my ridgerest at 14oz! I will have one ( or two) of these GG pads soon, I'll just have to figure out which one!

Also, if you do decide to try the GG pads, your comment about it pulling the ocf pad away from the hammock is applicable. The problem is easily solved for the GG pads, however. Take a short piece of the same shock cord......... The foot end is no problem for me and is not pulled away by the GG pad there.

Thanks for those tips! Did you say the SS could be used with a Speer type? With webbing straps? I'm just wondering how you would get the wide webbing thru the very narrow rope opening on one end of the SS?
Bill

[blackbishop351]

I thought I still had my thermo book but apparently I threw it away after that hideous class. But somehow I kept my astro book (must not have been buying this one back that semester ). So here are a few quotes about radiative heat transfer...

"With your eyes closed on a summer day, you can feel the Sun's heat beating down on you. But light and heat are only a part of the Sun's electromatic radiation..." (61). So we feel radiative heat transfer from the sun to our bodies in normal temps.

That radiation is generated by the fusion reactions in the sun (as in all stars) and gas temperatures around 4000K.

"Radiation or radiative heat transfer...involves the transfer of energy from one point to another through electromagnetic waves. If you've ever held your hand in front of a glowing space heater, you've felt radiative heat transfer" (322). So it also happens at temps that would heat up a room. And the new smooth-to stoves heat the pans through radiation since the heating element doesn't actually touch pan, right? Higher temps than a hammocker experiences but still not cosmic.

The heating elements in those stoves are MUCH hotter than the temperatures you set on the dials. Those stoves are also less efficient (and therefore take longer to heat) than diffusive-element stoves ("normal stoves") or convection ovens. Look around, by the way, and you'll see that convection ovens are pretty much the most efficient design out there - that's why most industrial kitchens use them rather than the conventional design.

One more example. When my kids get a high fever, I can hold my hand near their heads and feel the heat coming off. Heat is being transfered from their bodies to the environment, and then to my hand. That's radiation/absorption at normal living temps. (Well, a few degrees above normal, but still.)

Sure there's radiation at "normal" temps. I never said there wasn't. But if you could isolate the different transport mechanisms that are active between your son's forehead and your hand, and then looked at the amounts of heat being carried by each mechanism, you'd find that radiation is by FAR the least component.

In a real-life situation, all mechanisms come into play to some degree. That's why theory is nice - it allows us to concentrate on controlling one mechanism rather than trying to deal with them all.

As an afterthought, why is a radiator in a car called a radiator - it doesn't really radiate much heat away from the engine. It provides a larger surface area so convection can remove the heat as you drive. Odd.

I think the term "radiation", like so many others, is being used in a more general linguistic sense here - not the precise scientific definition.

[BillyBob58]

By the by - I just read Just Jeff's post over on another thread about the underquilt - I'm paraphrasing here. Sounds like all who get the SS and underpad:......................................... ......................4 - In the middle of your first cold night...before you've figured out the little details about adjusting it to your particular hammock/body/hang. WTF is this?! I have to get up AGAIN in this freezing weather for another 1/2" adjustment?! Frustration. (Hopefully you'll figure it out right away and get the adjustments down easily...if not, post back here and you'll get it figured out.)
.................You described what happens so well.

and it sounds soooo like getting the SuperShelter.

If this was all referring to SS and not underquilts, I must be missing something! I know I have talked about the learning curve of SS, but I was talking things like how to add clothing, pads or Garlington Insulators, etc to extend its range to 20 or below. Or trash bag ties or paper clips and fooling with the side elastics to make the pad stay diagonal.

But when it comes to the basic pad and undercover, I've never adjusted the
1st thing! I didn't know there was anything to adjust? I just run the suspension elastic cords thru the undercover and hang it from the already adjusted prussick rain fly connectors. That seems to hold it snug up against the hammock. Have I been doing something wrong? Could I have been getting even more warmth out of this design?
Bill

[Peter_pan]

Good point, TeeDee. But the same can be said from experience. A cat walking across a hot stove may learn to never walk on stoves again. His experience says stoves are hot. A smarter cat will wait until the stove cools off. (Paraphrased from a Mark Twain quote that I'm too lazy to look up.)

More to the point - I've never heard of anyone's experience with a space blanket where the space blanket's impact was isolated. "I was warm" is about as precise as they can get - then they mention the weather shield, other pads, etc, that were also involved.

I guess the most practical test would be to put the SS undercover w/o pad on the HH and see how warm that is. Then have someone slide the space blanket between the hammock and undercover (w/o the occupant getting out of the hammock) and see how much difference it makes. The gain in loft would be minimal, and the convection loss would be very close in both cases. Having someone else install the space blanket w/o the user moving means he won't lose his body heat so it'll be easier to "feel" the difference.

Just have to make sure the space blanket doesn't have any wrinkles when it's installed...that would act as loft and not isolate the space blanket's radiative properties.

We could also get some medical thermometers with those little EKG-looking sticky patches for measuring the temp change at specific locations between the user's body and hammock body.

But heat loss from evaporating condensation counteracts the heat gain from radiation...the question is how much. I don't know how we'd isolate the impact of condensation.

I've never heard that radiative heat loss only happens at high temps like BB says. I've actually heard that tarps help a bit by capturing radiative heat leaving the body. But regardless of whether the theory and experience of space blankets say they work or not, I'm pretty sure there are lighter and more convenient ways to get the same/better performance. That's my experience talking...with some non-scientific, undocumented, out-of-the-lab, backyard testing to back it up. Never took one into the field b/c I wasn't impressed with the performance.

I know Pan did a lot of testing before he and Smee designed the underquilts...I wonder if they have anything useful to add.

JJ, et al,

Yes we did do a lot of testing and experimentation.... all total we went though 18-20 different pad/mylar/fleece/wool combinations before we went to the under quilt route....

There were many outright failure and many close but no cigar results....

The out right failures were early attemps to use self inflatables in asym style nylon hammocks... pads squirted out every which way....best results were to put them in the bag, when the bag was big enough.... but then the classic worm dance to mount the hammock or get in and zip the bag ensued....No Gos all IMHO.

Blue pads and green Army pads were better.... still slipped some... shoulders and hips suffered.... multiple stacking was a pain that also had shifting problems.... duct taped helped but became messy... laced on wings tore the pad....bulk was a major detractor.... Without widening....definately No Gos

Early therorest, ridgerests were cut in half and taped back together crosswises to create 40x 24 with using the pack under the legs.... sweat pooling was so bad on a 600 mile section hike that I had to by fleece at a yard good shop and hand stitch a cover with dental floss to have an "absobant sheet"... polyester fleece stinks and won't become descented after a week... and the sweat puddles were still causing several night calls, though seemingly warm....Another major No Go.

Next were the Windshield pad experiments...about 4 different length and shape tests were conducted...Never could get below 52-55* in any of them...Least they were not bulky... they were also sweat pool generators...
We also had some tears, this was fairly common if the pad edges were trimmed... problem could be eliminated with duct tape... but then the sticky, rolling tape would get on you and the hammock....Below 55* they were No Gos... but low volume, weight and price was attractive....guess that is why we gave them multiple tries....

Mylar space blanket on the outside....was Thrice a failure.... first attempt was to mount by strings and shock cord....PITA to rig...noisy...by itself not very warm....Then used zip lock bags to form and hold a dead air space... little better.... hard to get in and out w/ a HH.... to fragile, too much time... again limited to 55-60 degree weather.... Eventually we glued Velcro on the space blanket and sewed corresponding patches on the hammock.... work reasonable until the wind picked up about mid nite, tore badly and we both froze....definate No Go.

Tried several small pads in the shape of T or I.... limited to 60*....Pushed it on a Vetrans Day weekend hike and froze again... No Gos for the ULpad approach.

Wider pads were somewhat successful... had to learn to place them well, it worked.... but they became bulky....and, I was again plagued by the sweat pool issues.... No Gos

Tried a couple variants of fleece blankets both inside the hammock and as UQ...inside sucked as they balled up and got uncomfortable... had to keep re straightening or freeze.... outside was marginal, again secured by velcro... tennded to sag away....55-60...No Gos.

Wool blankets were tried in the hanmmock.... tack stitched to the corners... minimized shifting.... very heavy...again 50 degree range was best results... No Go, especially considering the weight.

Must add all this was before the SPE, which is the best pad manager... results are good but bulk is still a factor... not as comfortable as a bare hammock and for me and others back sweat on pads is still an issue.... But it remains the best pad manager IMHO.

Also must add this was all before the now readily available wider pads from Speer, Oware and GG... They work... they have their limits... some have reasonable luck stacking them.... but as a back sweater I consider them problematic and uncomfrtable at best.


We gave up in November 2003 and turned to the Down Under Quilts....Hanging on a Bluff high above the James River in late December...30 degrees...rain and sleet ... two 50+ year old men slept 8 hours strait thru without even a p break... these were 2 inches of loft below us and 2.5 above us .... socks , lj and a skull cap.

Sales began the following Spring with the first batch totally sold out before Trail Days 2004 which we vended as order takers....

And yes this was all before the intro of the HHSS....And Yes we did get a HHSS and try it also.... We still prefer UQs... but then we are biased.

Couple general notes on testing....
Lab like testing is expensive and of limited value.
Most comparisions posted on these forums involves apples vs oranges as they are disimiliar system capabilities or the are made "equal" by the addition of mylar blankets, leaves, extra pads etc....
Before any testing the parameters to be evaluated/compared should be defined...
Test conditions should be as equal as possible.
Weighting of parameters is best done by each individual as each will have their own values and priorities....ie one may value low cost highest, while another may value warmth, or yet another may waqnt to reduce bulk...let the test/comparisions post the facts and the reader asign the values... (FWIW, BPL does as good job as any in conducting evaluations and reporting against these standards as any IMHO).

In the end there are options and opinions.... everyone must HYOH and hyoh(hang your own hammoch)...

Read all the "Forum reports" in these threads with and eye for detail, an open mind, and a caution that amost all are biased, even if only in the vanity view of their system is best/great.

Good night...time to turn-in.

Pan

[BillyBob58]

Very informative/useful post, Pan! I may yet end up with an underquilt or Peapod one of these days. The reason I got a SS was because I didn't know there were any other options besides a pad in the hammock! I bought the HH, didn't even know there was any other kind of backpackers hammock. Found out about the SS while buying the hammock, and got them together. Hated it at first, but have learned to make it pretty usable.

Did you have the pad/sweat problems when you used to sleep on the ground? I never had that problem with a pad under my bag on the ground, and so far not in a hammock on an SPE. I wonder if that's because, at least if it's cold, I tend to wear light fleece inside my bag, in the hammock or on the ground?

[Just Jeff]

With a pad on the ground, the pad stays flat. In a hammock, the pad curves around you and hugs your body...removing any chance of ventilation and giving you a vapor barrier on the part touching the pad. That's why moisture management is more important in a hammock than on the ground if you're using pads.

Like Pan, I have moisture problems when I use CCF pads. But for some reason, I don't get the same moisture problems with the Exped Downmat 7. It's still non-breathable and very warm so I'm not sure what causes the difference. My best guess is the Exped's covering.

BB - so when I can feel the heat radiating off of my son, what's the heat transfer modality? Not evaporation or conduction. Convection? But it has to get into the air to cause a current. Which leaves radiation as the primary. Now if I could catch all that heat radiating from him and send it back towards him (like space blankets claim to do), that would be useful for insulating hammocks.

Even so, it seems that the primary use for a space blanket in the field (for general use as they're intended...not what we're talking about here) is to stop convection and provide a vapor barrier. (Risk did some tests with garbage bags and found they did a pretty good job of trapping heat...same deal, proving the same point, just w/o the radiation.)

The difference is that, in a hammock, you've already got a convection block (pad, SS undercover, underquilt, etc). So the primary modality for a space blanket is already being carried...leaving only radiation as its contribution. And, IMO at least, the amount of heat returned by radiation from a space blanket doesn't justify the hassle and weight. (OTOH, if you were truly using it as an emergency blanket as it's designed, and that's all you were carrying, you'd get the convection block, the vapor barrier and the radiation...it might justify itself.)

I guess that bold part is a more clear answer to TeeDee's question about why I don't like space blankets than the one I posted earlier.