PLUQ question from a newbie

[Moondog55]

I don't think I've ever had a cold spot when sleeping on a cot, and seldom in the last 30 years on snow; not since I came to the late realisation that my mattress and base insulation was more important than my quilt insulation.
I insulate the underside of my cots with a combination of a cot skirt to keep out the breeze and a polyester blanket underneath the cots base with a 50mm airgap between the poly blanket and the cot canvas. I was thinking [ did think ] that underquilts worked in the same way. In summer I don't use the skirt and under blanket, just an uninsulated airmat
Please enlighten me as I just don't get this at all.

[sidneyhornblower]

Please enlighten me as I just don't get this at all.

I think what Goobie is getting at is mainly this. In a hammock underquilt system, an air gap between the hammock and the insulation underneath is not dead, trapped air. It is a leak that loses you your warmth. Many of us have experienced this many times with different setups. In a ground system, air underneath you can be held in by the ground. Not so under a hammock, where air is free to circulate beneath your insulation. I've had this happen mostly in my bridge hammock setups. Like you, I thought that if the underquilt sagged away from the hammock, so what? The air between the underquilt and the hammock would just add to the insulative value. I was wrong, badly wrong.

That air gap will pull warmth from your body by convection and then slowly lose it through the underquilt to the open air below. Put another way, your body heats up the air gap between the hammock and underquilt. The air in that gap then has to heat up the underquilt, which is exposed to the open air. It becomes a losing battle, especially if there's the slightest breeze.

You are correct that dead air has some insulative value. Where you're going wrong is assuming that the air gap between the hammock and underquilt is dead. It's not. If it's big enough (and it doesn't take much) it becomes more than enough to pull body warmth away from you by convection. How much and how long it takes is highly dependent upon the ambient temperature, wind speed, your personal metabolism and the size of the air gap.

[Moondog55]

AH Lightbulb moment
So If I want that trapped air to work as insulation then the underquilt needs to be fully perimetre sewn or snapped on to the hammock edges not so deep and I'm part way to making a PeaPod. Sleeping on the ground is so much less complicated.

[LowTech]

The UQ doesn't have to be attached, touching works well enough in most situations. Ground sleeping may seem less complicated but I find floating in a sleeping bag (what happens w/ a good, well adjusted, UQ and TQ combo) to be easy, simple, and far more comfortable.
If I'm after warmth then I want my "bag" to be close to my body and not w/ a lot of air space between me and the insulation, same w/ quilts. I want the insulation under me to be touching me the same as the insulation on top of me. The thin layer of nylon that makes up my hammock is almost irrelevant in that it's the only thing between me and the lower part of my "bag", the UQ. Air gap there or between me and the TQ is undesirable.

"Sent w/o me knowing"

[cougarmeat]

An Under Quilt Protector (UQP) acts the same way as your cot skirt worked and has the same purpose (and more). Because I have a few hammocks and UQ's and mix and match, I don't have one "setting" for the hammock/UQ. Because I'm the only one setting up, I can't be in the hammock and outside checking things at the same time. A UQP makes that adjustment a little less critical. When I started with a Hennessy Expedition in the summer. I just put my Thermarest Guide inflatable in the nylon component of the SuperShelter (which was essentially a UQP). The pad wasn't pressed against the body of the hammock but the combination created and warm air pocket.

It worked just fine for that season.