Originally Posted by DaleW
You're thinking open-ended underquilts. I'm thinking undercovers with insulation inside. And I have to admit, anything I make will have synthetic fill, and everything is pretty well battened down. I am thinking full or at least 3/4 coverage too.
With an undercover and the quilt attached to the bottom of the hammock on all four sides, there is no droop. If you must, the insulation can easily have drawstrings in the ends, but with Velcro fastening to the hammock bottom, I don't know where it can go.
If there is a weak point in fastening the UQ to the hammock, it is at the top edge near your left shoulder and right of your feet, where there will be a couple inches of stress on top of the insulation, which may compress it a bit. Your top quilt should be doing the job, but if not, maybe it needs a little foam or Insultex "bumper" in those areas. The outer cover should be good 'n loose in those areas too.
And you don't have open air gaps with the under cover. There is no opportunity for moving air to get to the middle/bottom where things tend to sag. You have one more layer in play vs an add-on UQ if you are putting quilted down insulators in there.
If the insulation's weight manages to push the UC downward more than the insulations ability to loft up and fill the space between the UC and hammock, there might be a problem. And more so if the UC is not very well sealed at all edges and the end, leaving an open path for cold air to flow downward and fill that even very small gap between your back and the insulation. Both the distance between the weighted ( with insulation) UC- after laying in the hammock- and the amount/loft of the added insulation will have either be just right- or adjustable. Obviously can be done with Velcro or snaps, but it will need to be pretty custom.
A Speer PeaPod- when fully or mostly closed- is supported by the nylon cords that tie it to the ends of the hammock, AND by the top side Velcro closure along the entire length. I adjust mine so that either, once I lay down, the bottom inside is barely in contact with my back, or if I want to add a jacket something for more loft, it has an inch or 3 gap after I lay down, but before adding extra insulation. ( or an unfilled gap if it is kind of warm out) That means I either start out with a 4-6" gap between the pod and un-occupied hammock, or more if I plan on adding something. if after I am in, I see that it is either too tight (compressing loft) or to loose with too much gap, I just get out and make one small adjustment on one end. Mostly, I never even have to do this. Once all of this is done, it will stay put due to the non-elastic end cords and the full length Velcro closure, pretty much ending any worries of any thru the night sag. Also, as it is cinched tight around the hammock on the ends, and closed as tightly as desired along the top, with thick loft draping over the hammock edges and down onto the user, there really won't be any cold air rushing in to fill any unintended gap under your back.
True it is added on, but it sure has been bomb proof, on more than one brand of hammock, for me. I just has not failed me up to 10F below it's rated temps, with addition of either puffy clothing or a 40-50F TQ and a space blanket below.
The insulated hammocks are interesting concepts, though they have all been DIY. That will save the weight of one layer of nylon. Just a larger layer of nylon sewn to the hammock and filled with insulating material. But venting in warm weather MIGHT be a problem, I suppose?