Originally Posted by senecio-joe
I think I might be missing something on how insulation works. I understand that I am the heat source putting the air into the down in the UQ which then traps that warm air.
If I then put a foam pad with an R value of say R2 or R3
between the heat source and the down of the UQ I will be blocking heat
from getting to the down to warm it up. The heat then has to radiate back
up through the R value of the pad.
I feel that the combination of both would be warmer but I don't know why.
It seems to me that if the foam pad was below the down it would be more efficient but hard to do. And then there would be a condensation problem
which is even more difficult to understand. Maybe open cell foam below
the down would work. Maybe the answer is forget the foam and go with more down. More down seems a good answer for all problems.
It feels nice, but I'm not sure it is needed to actually radiate the heat back up through the pad- or quilt. As long as the heat is prevented from leaving your body and traveling to the outside cold air where it "disappears" to then be replaced by more of your body's heat, the job is done.
If adding the pad was going to be a problem because "will be blocking heat from getting to the down to warm it up.", then a thicker UQ would be the same problem, seems to me. IOW, the thicker your quilt, the less you would be able to warm up the outer layers of your quilt and then benefit from that heat being radiated back to you. I think the over all idea is that there is a buffer zone of dead air that is difficult for warm air to travel across to disappear into the cold air. The colder the outside air and greater the differential with your warm body, the thicker the layer needs to be to keep them apart.
Here is another way to look at it: You say you are concerned that you are unable to warm your quilt up due to interference from your pad? And then that warmed up air in the quilt can't get back through the pad to your back, even if it was warmed up to start with? Well then that must mean that your bodies heat has not gone anywhere, and it is right there under your back and just inside your pad. If it gets colder, and the differential from warm to cold becomes greater. then maybe it can get through that pad and then is stopped in the quilt, warming it up. But in the meantime, your quilt is cold BUT all of your bodies heat is only about 1/4 to 1/2" away from you, trapped in your pad. You have a warm pad in contact with your back.
Shouldn't that be just as effective as your bodies heat radiating several inches further into the outer layers of your quilt and then having it "radiate" back up to your back?
Remember, a thick enough pad by itself can take you to extreme temps. There are folks here who have used only CCF pads to way below zero F. One of my few times on pads - two summer rated pads stacked- was the toastiest night yet in a hammock. While it was only 18F, I was so warm I clearly could have gone quite a bit lower with a 1" thick torso length inflatable Thermarest "Ultralight" on top of a full length Ridgerest. The main reason to not use a pad in a hammock are comfort and sweat/condensation issues for some folks. But keeping warm with a pad is not a problem, at least for some folks.
But adding a pad can for sure significantly boost an UQ. I have a friend that puts various pads under his hammock down in a 45-50*F rated Pea Pod and sleeps toasty in the 20s so far, no problem.