405Re: Hammock Camping Franken pad and bride of Frankenpad
- Feb 2, 2003That's why I said slightly warmer. I would be interested if anyone
has tested how warm a space blanket is compared to say a waterproof
silnylon "space" blanket.
I'll have to admit I'm not as smart as NASA engeniers except for
--- In email@example.com, "Ernest Engman"
> If reflective pads are so good, then why not a sleeping bag thatis made
> from them? They aren't. Can a space blanket really work? Somewhat,but
> I've never bet my life on one and will never do so because thetheory
> that tells you they will is very flawed. But people buy them, sopeople
> will sell them.over
> My position that radiant heat reflectors are snake oil has grown
> time, and after a couple of debates with some people smarter thanI, I'm
> sure of it.an
> The science is this, and don't take it is as just me, this is from
> aerospace engineer working for NASA and another engineer that haveboth
> convinced me of this:night
> Heat isn't as simple as saying 25% of your body heat is lost thru
> radiant heat loss. It is much more complicated than that. On a
> with high humidity but low temperature, you will be a lot colderthan on
> a night with the same temp with lower humidity. Why? Because thewet
> moisture in the air is conductive, same principle as sleeping in a
> bag in a way, but you are loosing more of a percent of heat thisway and
> less thru radiant heat. Same thing in high winds. How can higherwinds
> make that big a difference if more is lost thru radiant heat loss?It
> couldn't but the real problem is demonstrated by this isconvective heat
> loss. I hope this isn't too much of a tangent for the discussion,but it
> just shows how one factor can change the percentages.not
> Radiant heat reflectors (actually insulators) were made to work in
> space. In space there isn't any air flow at all to worry about, so
> absolutely no convective heat loss to worry about. In space they
> only have to protect the person from heat loss, but excessive heatgain
> from solar radiant heat. Ever hear that in space one side willfreeze
> while the side facing the sun would burn up?the
> So what is heat? Heat is energy, cold isn't the opposite, it is the
> absence of heat. Heat energy, by its nature, will try to equalize
> energy from places of higher energy to places of lower energy. Ifyour
> body is the point of higher energy (which it normally is at night)then
> your heat energy will attempt to displace outward.your body
> There are about 4 means of heat loss that you must worry about.
> 1. Evaporation. When you sweat or breathe, the water loss from
> carries heat energy with it. To prevent this you can wrap yourselfin a
> vapor barrier. But to make this work, you will most likely want tobe
> totally undressed or you will end up in soggy clothing which isalso
> bad. Ed talks about always allowing your breath a way to get out -very
> 2. Radiant heat loss (the main topic) which is heat transfer based
> how IR opaque or transparent barriers between you and the objectare. If
> you were to stand naked in a freezer, you would loose a great dealof
> body heat thru radiant heat loss. Wrap yourself in a spaceblanket, and
> you would reflect about 50% of your heat loss back at yourselfbecause
> the air will still carry away some through convection. But toreduce
> this loss, you can wear clothing. Since the clothing isessentially IR
> opaque, you can reduce this loss of you radiant heat energy down todisagree
> about 5% of your original loss. So if you have a given (which I
> with) of 25% heat loss thru radiant heat, and reduce that to 5% ofthe
> original loss by wearing clothing, then you are down to less than2% of
> your total body heat loss. Now use a radiant heat reflector tocapture
> 50% of that, and it is returning less than 1% of your total bodyheat
> lost. This 95% (give or take) heat loss prevention occurs for everyaround
> layer of IR opaque material between you, and the colder objects
> you. So if you wear clothing, then a sleeping bag (inside layer)then
> you already have reduced your IR heat loss to less than 1%.need
> For a radiant heat reflector to work (in the atmosphere) you would
> to be inside it without clothing and not touch it (which is whereI'm
> going next) for it to be of any help. Interestingly Stephensonswell for
> Warmlight sleeping bags understands this and explains it quite
> someone looking at their bags.turn
> To prove this, feel free to make a shower curtain of mylar then
> your heat off. Stand inside the shower with the curtain nude andsee if
> it (the curtain) gets warm. It won't. You are not a big enough anand
> emitter of IR to make it work. The sun is a huge IR heat emitter
> does this quite well, unfortunately our bodies don't come with ahuge
> supply of self heating hydrogen.carries
> 3. Convective heat loss. When air passes around your body, it
> away heat; this is the biggest problem keeping warm in anatmosphere.
> The trick is to stop air from passing around you and createpockets of
> still air that can be warmed and kept into place. Sleeping bagsand pads
> are designed to do this. Again, if radiant heat reflectors weretruly
> beneficial, then that is how we should have been staying warm forthe
> last 50 years in the hiking world, but so far we all still usesleeping
> bags and pads. Ed has done a great job of figuring out how to makethis
> happen with a pea pod. And to make it even better would be tosurround
> the pod with a waterproof material that totally stopped any airfrom
> getting out and totally stopped any moisture from getting out.Foil wrap
> does a great job of this, by the way - that is what a spaceblanket is
> made from. But it also has a drawback that it traps moisture thatmaterial
> destroys loft in a down bag. The best solution would be some
> that could surround your pea pot and prevent air flow in, stripheat on
> the way out for moisture, and wouldn't suffocate you.away. This
> 4. Conductive heat loss. This is a problem because some people try
> laying directly on the reflective surfaces which are also excellent
> conductors. Some spots under these conductors are warm because they
> prevent evaporation or convection, but they also conduct heat
> is also how the moisture carries away your body heat.to.
> So to conclude this lengthy post and spark the debate I don't mean
> Radiant heat reflectors are not that inside the atmosphere, theyare
> serving as barriers to convective heat and if used right,evaporative
> heat. I've never said that people using a system that involvesa "Heat
> Rflector" aren't staying warm (heck I have one) I'm just sayingthey
> should get smart about why they work and figure the bestapplications
> for these materials. Aluminized plastic (mylar) is very good atblocking
> moisture, and it is what all really long shelf life packet foodsare now
> packed in.be
> Ernest Engman
> AKA SGT Rock
> -----Original Message-----
> From: starnescr <starnescr@y...> [mailto:starnescr@y...]
> Sent: Sunday, February 02, 2003 1:37 PM
> To: firstname.lastname@example.org
> Subject: Re: Hammock Camping Franken pad and bride of Frankenpad
> If a reflectic pad is snake oil then why are "emergency blankets
> made of reflective material. Of course you wrap a space blanket
> around you and are not laying on it only. Would a reflective pad
> more effective (no mater how unpracticle) if it went all the waypad.
> around you. I think the reflective pad is somewhat usefull if you
> are not laying directly on it. From what Tom Hennessy and others
> have said there needs to be a little space between the heat source
> and the reflective surface. Hence my fleece covered reflectic
> A 1/2 inch closed cell foam pad the same size as mine would bepad
> heavier but I'm not sure how much. I'm not saying a reflective
> is the answer either. I just believe given the same R value aSee
> reflective pad would be slightly warmer.
> Coy Boy
> --- In email@example.com, "Ernest Engman"
> <ebengman@h...> wrote:
> > The pad I use serves a couple of purposes.
> > 1. Wind/air barrier. It is made of aluminum coated close cell
> > pad. I can use it alone in cool but not cold temps by turning it
> > side down and preventing air circulation.
> > 2. Since it is also foam, it adds a light and small layer of
> > insulation.
> > 3. It serves as a ground pad under the hammock when I lay it on
> > ground to stay warm. It is wide and long enough for that. Often
> > having to do this, the ground isn't dry and no sense getting the
> > wet.
> > 4. Closed cell foam pads work better against a non-breathable
> > barrier than against a breathable material like than hammock.
> > excellent post by youngblood:
> > http://hikinghq.net/forum/showthread.php?
> > ff2
> > <http://hikinghq.net/forum/showthread.php?
> > bff2&threadid=359> &threadid=359
> > I say heat reflectors are snake oil, because the science that
> > are a radiant heat reflector for someone sleeping in a hammock
> > flawed.
> > Ernest Engman
> > AKA SGT Rock
> > sgtrock@h...
> > <http://hikinghq.net/> http://hikinghq.net
> > -----Original Message-----
> > From: David Chinell [mailto:dchinell@m...]
> > Sent: Thursday, January 30, 2003 9:25 AM
> > To: firstname.lastname@example.org
> > Subject: RE: Hammock Camping Franken pad and bride of Frankenpad
> > Sarge: Thanks for the R&D work. I'm dreaming along the same
> > That's what the evazote "shawl" is about -- extra width betweenuse
> the hips
> > and shoulders.
> > But I need to make a cloth casing to hold the wings so they're
> > detachable, rather than permanent, so I can roll it all up in a
> > 24-inch wide roll. How do you pack the Frankenpad?
> > And if, as you say, "heat reflectors are snake oil" why do you
> > windshield reflector? Why not just another pad?
> > Bear
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