Under quilt question. Physics or Perception?

[matted]

This is not “camping” related as I would certainly have an UQ or pad with me whenever I plan on sleeping below ~75F or so, but this is mostly me ruminating and trying to understand something…

I have noticed that when lounging in a hammock without insulation (top OR bottom insulation, in a WB RR, Superior DayLite, whatever…), let’s say in temps between 50-70 degrees, that the slightest breeze makes any part of me in contact with the hammock feel like it is up against ice. CBS galore! I understand that this convective cooling is why we need an under quilt, but what I’m trying to understand is why only the parts of me that are in contact with the hammock feel this… if I was standing upright in the same breeze, I would not feel that same coolness. Is this because:

a) physics; something to do with my weight compressing my clothes or whatever little insulation I have which renders it less effective

or

b) perception; usually when sitting in a chair, or lying on a day bed, blanket, etc, whatever we are in contact with either has some effective insulation or at least blocks the wind from convectively cooling whatever part of our body is in contact with whatever is supporting our weight. Could it be that my brain just isn’t expecting those parts to feel cool, as opposed to standing in the same breeze, where it expects it?

or

c) I’m way off base and it is due to _________ reason.


Please help me understand. Thanks in advance!

[TominMN]

I'd say it's mostly a). In addition, the hammock side is probably providing a bit of a wind block for the rest of you.

FWIW, wind effect is NOT convection. (And convection ovens really aren't!) Convection is the rising of heated fluid/air and the falling of that which is cooler. I suppose if you take in the atmosphere as a whole, then sometimes wind is the result of replacing warm air that has risen.

Wind pushes away the warm air "cushion" around a warm object/substance and causes much more rapid conductive and radiative heat transfer to the, now, cooler adjacent air.

Convection is often identified as a form of heat transfer. I would argue that convection is the movement of a heated substance, which acquired heat via conduction and/or radiation.

Not trying to pick on you. I see this misconception in the forum regularly. This isn't splitting hairs; it's simply trying to be precise.

(I could get going about condensation. Let's not get me started!)

[matted]

Thanks for the reply! And for the correction as well. Today I learned!

Cheers

[deadeye]

I agree it's (a). That little bit of air space between you and your shirt provides dead air insulation, which is lost when pressed against the hammock fabric. Those of us that shave our heads understand how effective even just the air trapped by a 1/4 inch of hair is compared to a clean shaven scalp.

[Vryce]

I would also like to point out that the material of most hammocks is very "slick" to the touch. This allows to wind to move over the surface more easily allowing a more effective transfer of heat. Most "cloth" clothing isn't as slick which is why you don't lose heat as fast. Insulation relies on dead air to prevent heat transfer. If the air you warm up around you doesn't move away you will stay warmer. But to answer your question of it being Physics or Perception, well it's both. The hammock does increase the heat transfer without insulation under you, but your perception of the heat transfer is unique to you. Meaning that you may perceive more or less heat transfer than someone else in the same situation.