uninsulated air mattress R value?

The R-value of a simple airspace like this is 1.0. In general, air spaces from very small (ie. 0.5") up to quite large (ie. 8") are all basically 1.0. So this would be good mainly as a summer pad.

Yup, R = 1. FYI, that's what Bender claims it to be on an uninsulated pad.

I say they should reevaluate the R scale. 0 should be thermally neutral. (I think what is assumed to be R5?) Since uninsulated pads actually cool down shouldn't the negative temp levels get counted for. In this system most pads would be a negative. An Exped DAM or Bender's R6 would be positive. I guess then there would have to be a "standard of movement" or something that actually facilitates the convective cooling. Aaahhh I guess it wouldn't work…

"this pad is a -4R pad at 4 turnovers/ night" WTF?

I don't know if R = 5 is thermally neutral, but I'm skeptical. If something with an R value of 5 was thermally neutral, you wouldn't need anything with an R value 6 or higher, no?

Given the nature of insulation, if 0 was thermally neutral I don't think you'd have any pad with an value above 0, unless it had some sort of powered heater built in.

If you are 100F, the ground was 30F, and your pad was thermally neutral wouldn't the pad 'feel' like 65F? Having a higher than neutral pad would allow you to maintain a temp closer to your body's. A less than neutral pad would favor the grounds temp and be colder.

You can overheat with too much insulation, why would that not apply to a pad?

Right? Scientists?

How does it work? Don't you love that question

You have to go back to Richard's chart:

http://www.backpackinglight.com/cgi-bin/backpackinglight/xdpy/forum_thread/9378/index.html

one clo = 0.88 R

R value = difference in temperature across the insulation / heat flow

= difference in degree F / heat flow in BTU/ft2*hr

the chart assumes the heat flow is fixed for a particular activity level, like when you're sleeping

the chart tells you what clo (or R value) needed for a particular temperature

of course, you'de have to average pad, sleeping bag,…

and the ground temperature is different than the air temperature

if the R value is larger, then your skin temperature would raise and at some point you'de start sweating to cool off

if the R value is smaller, then your skin temperature would lower which would be uncomfortable – your body would increase heat flow some to compensate, like sending less blood to arms and legs or shivering

+1 what Jerry said.

One way to sum up what Jerry said with the R value calculation is that what is comfortable to an individual is dependent on the temperature difference between the body and the air and ground.

All pads are less than neutral. If a pad was thermally neutral- a perfect insulator- you would quickly overheat.

The surface of a pad would feels pretty close to skin temperature in a comfortable situation. What keeps it at that temperature, rather than loosing heat to the environment or accumulating heat from your body, is having insulation that is appropriate for the air/ground temperature. Just as true for a pad as it is for a jacket.

Hmmmm I thought I read here something about that people shoot for r5 for winter apps because it was neutral. Apparently neutral is not the case, its just at a high enough value to insulate on snow.

Maybe its just semantics- I'm saying 'neutral' which sounds like it will buffer any two differences in temp; whereas, its really more like 'enough' to buffer snow and a human.

I guess neutral would depend on the temps of the two bodies you are separating? Change one body for a colder one and the pad becomes 'less than neutral' for that application? (from ground to snow)

So if I slept on a r1 pad and was comfortable at a given temp, then I switched out for an R7 I wouldn't overheat?

If you're on snow, maybe it's 32F.

From Richard's chart you want a clo of about 6.1, which is an R of about 5.4, which is close enough to the R 5 value you mentioned.

For R 1, you'de be comfortable at about 85 F (from Richard's chart)

If you switched to R 7 you'de probably be too warm

Of course it's more complicated than that because you have to average over your pad and sleeping bag, and you gradually warm up the ground and it has insulation value,…