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405Re: Hammock Camping Franken pad and bride of Frankenpad

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  • starnescr <starnescr@yahoo.com>
    Feb 2, 2003
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      That'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
      maybe Gordo.

      Coy Boy

      --- In hammockcamping@yahoogroups.com, "Ernest Engman"
      <ebengman@h...> wrote:
      > If reflective pads are so good, then why not a sleeping bag that
      is 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 the
      theory
      > that tells you they will is very flawed. But people buy them, so
      people
      > will sell them.
      >
      > My position that radiant heat reflectors are snake oil has grown
      over
      > time, and after a couple of debates with some people smarter than
      I, I'm
      > sure of it.
      >
      > The science is this, and don't take it is as just me, this is from
      an
      > aerospace engineer working for NASA and another engineer that have
      both
      > convinced me of this:
      >
      > 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
      night
      > with high humidity but low temperature, you will be a lot colder
      than on
      > a night with the same temp with lower humidity. Why? Because the
      > moisture in the air is conductive, same principle as sleeping in a
      wet
      > bag in a way, but you are loosing more of a percent of heat this
      way and
      > less thru radiant heat. Same thing in high winds. How can higher
      winds
      > make that big a difference if more is lost thru radiant heat loss?
      It
      > couldn't but the real problem is demonstrated by this is
      convective 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.
      >
      > 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
      not
      > only have to protect the person from heat loss, but excessive heat
      gain
      > from solar radiant heat. Ever hear that in space one side will
      freeze
      > while the side facing the sun would burn up?
      >
      > 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
      the
      > energy from places of higher energy to places of lower energy. If
      your
      > body is the point of higher energy (which it normally is at night)
      then
      > your heat energy will attempt to displace outward.
      >
      > There are about 4 means of heat loss that you must worry about.
      >
      > 1. Evaporation. When you sweat or breathe, the water loss from
      your body
      > carries heat energy with it. To prevent this you can wrap yourself
      in a
      > vapor barrier. But to make this work, you will most likely want to
      be
      > totally undressed or you will end up in soggy clothing which is
      also
      > bad. Ed talks about always allowing your breath a way to get out -
      very
      > important!
      >
      > 2. Radiant heat loss (the main topic) which is heat transfer based
      on
      > how IR opaque or transparent barriers between you and the object
      are. If
      > you were to stand naked in a freezer, you would loose a great deal
      of
      > body heat thru radiant heat loss. Wrap yourself in a space
      blanket, and
      > you would reflect about 50% of your heat loss back at yourself
      because
      > the air will still carry away some through convection. But to
      reduce
      > this loss, you can wear clothing. Since the clothing is
      essentially IR
      > opaque, you can reduce this loss of you radiant heat energy down to
      > about 5% of your original loss. So if you have a given (which I
      disagree
      > with) of 25% heat loss thru radiant heat, and reduce that to 5% of
      the
      > original loss by wearing clothing, then you are down to less than
      2% of
      > your total body heat loss. Now use a radiant heat reflector to
      capture
      > 50% of that, and it is returning less than 1% of your total body
      heat
      > lost. This 95% (give or take) heat loss prevention occurs for every
      > layer of IR opaque material between you, and the colder objects
      around
      > 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%.
      >
      > For a radiant heat reflector to work (in the atmosphere) you would
      need
      > to be inside it without clothing and not touch it (which is where
      I'm
      > going next) for it to be of any help. Interestingly Stephensons
      > Warmlight sleeping bags understands this and explains it quite
      well for
      > someone looking at their bags.
      >
      > To prove this, feel free to make a shower curtain of mylar then
      turn
      > your heat off. Stand inside the shower with the curtain nude and
      see if
      > it (the curtain) gets warm. It won't. You are not a big enough an
      > emitter of IR to make it work. The sun is a huge IR heat emitter
      and
      > does this quite well, unfortunately our bodies don't come with a
      huge
      > supply of self heating hydrogen.
      >
      > 3. Convective heat loss. When air passes around your body, it
      carries
      > away heat; this is the biggest problem keeping warm in an
      atmosphere.
      > The trick is to stop air from passing around you and create
      pockets of
      > still air that can be warmed and kept into place. Sleeping bags
      and pads
      > are designed to do this. Again, if radiant heat reflectors were
      truly
      > beneficial, then that is how we should have been staying warm for
      the
      > last 50 years in the hiking world, but so far we all still use
      sleeping
      > bags and pads. Ed has done a great job of figuring out how to make
      this
      > happen with a pea pod. And to make it even better would be to
      surround
      > the pod with a waterproof material that totally stopped any air
      from
      > 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 space
      blanket is
      > made from. But it also has a drawback that it traps moisture that
      > destroys loft in a down bag. The best solution would be some
      material
      > that could surround your pea pot and prevent air flow in, strip
      heat on
      > the way out for moisture, and wouldn't suffocate you.
      >
      > 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
      away. This
      > is also how the moisture carries away your body heat.
      >
      > So to conclude this lengthy post and spark the debate I don't mean
      to.
      > Radiant heat reflectors are not that inside the atmosphere, they
      are
      > serving as barriers to convective heat and if used right,
      evaporative
      > heat. I've never said that people using a system that involves
      a "Heat
      > Rflector" aren't staying warm (heck I have one) I'm just saying
      they
      > should get smart about why they work and figure the best
      applications
      > for these materials. Aluminized plastic (mylar) is very good at
      blocking
      > moisture, and it is what all really long shelf life packet foods
      are now
      > packed in.
      >
      > Ernest Engman
      > AKA SGT Rock
      > sgtrock@h...
      > http://hikinghq.net
      >
      >
      >
      > -----Original Message-----
      > From: starnescr <starnescr@y...> [mailto:starnescr@y...]
      > Sent: Sunday, February 02, 2003 1:37 PM
      > To: hammockcamping@yahoogroups.com
      > 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
      be
      > more effective (no mater how unpracticle) if it went all the way
      > 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
      pad.
      > A 1/2 inch closed cell foam pad the same size as mine would be
      > heavier but I'm not sure how much. I'm not saying a reflective
      pad
      > is the answer either. I just believe given the same R value a
      > reflective pad would be slightly warmer.
      >
      > Coy Boy
      >
      > --- In hammockcamping@yahoogroups.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
      > foam
      > > pad. I can use it alone in cool but not cold temps by turning it
      > shiny
      > > 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
      > the
      > > ground to stay warm. It is wide and long enough for that. Often
      > when
      > > having to do this, the ground isn't dry and no sense getting the
      > fabric
      > > wet.
      > > 4. Closed cell foam pads work better against a non-breathable
      > > barrier than against a breathable material like than hammock.
      See
      > this
      > > excellent post by youngblood:
      > > http://hikinghq.net/forum/showthread.php?
      > s=10900e520cfd29662ed8485b43feb
      > > ff2
      > > <http://hikinghq.net/forum/showthread.php?
      > s=10900e520cfd29662ed8485b43fe
      > > bff2&threadid=359> &threadid=359
      > >
      > > I say heat reflectors are snake oil, because the science that
      says
      > they
      > > are a radiant heat reflector for someone sleeping in a hammock
      is
      > highly
      > > 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: hammockcamping@yahoogroups.com
      > > Subject: RE: Hammock Camping Franken pad and bride of Frankenpad
      > >
      > > Sarge: Thanks for the R&D work. I'm dreaming along the same
      lines.
      > > That's what the evazote "shawl" is about -- extra width between
      > 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
      > single,
      > > 24-inch wide roll. How do you pack the Frankenpad?
      > >
      > > And if, as you say, "heat reflectors are snake oil" why do you
      use
      > a
      > > windshield reflector? Why not just another pad?
      > >
      > > Bear
      > >
      > >
      > > To unsubscribe from this group, send an email to:
      > > hammockcamping-unsubscribe@yahoogroups.com
      > >
      > >
      > >
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      > > <http://docs.yahoo.com/info/terms/> Terms of Service.
      >
      >
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