JJ's answer about the flat pad on the ground and the compressed bath tub wrap in the hammock is the difference.....No,I don't have a noticible back sweat issue on the ground. ... Though I haven't been to ground sice spring 2003.
Sweaty back is worth thought.... My notes to newbies is to ask these questions. " If you sit on a naugahyde chair in a conference, or say church service, in a neutral to warm room for an hour; when you rise are you pulling a sweat soaked shirt off your back (most noticible for the non-tshirt wearers)? ...Do you look for a wall to stand against so you can pull your drawes free(TMI?), or do the descrete leg out stretch/twist? If you have had these experiences...then you will experience the sweaty back issues on pads to some degree when used in a hammock.
Youngblood and I have had some discussion on this sweaty back issue in years past....He has theory that this is caused by over heating and that proper venting of the top will eliminate the issue.... While I agree that over heating definately exaccerbates the issue... in my experience, venting and reducing comfort to the neutral temp state does not eliminate the problem because approximately 50 percent of the body when effectively pad wrapped is not vented and like the chair test with full 85-90 percent of the body vented the close contact, non breathing 15 percent is still a problem.
Your comment on the wearing of fleece is noteworthy also... When I used fleece to limit the sweat moisture....the fleece wicked away athe puddle....but, it became damp and less effective itself.... in warmer weather if I changed first on rising, it meant I packed a heavier sweated up fleece (note this can be mitigated by wearing it dry for 30 minutes or so in the AM).... same effect as the fleece pad cover I noted in the failed experiments post.... will say that wearing fleece is preferable to laying on a fleece blanket IMHO for both comfort, elimination of hassles and multifuncionality of separate garments..... BIG NOTE.... for those going this route, and for trips over a day or two.....I personally have switched from fleece to all merino wools....competitive in weight.... FUNK FREE.... warmer....equally compressable.... just pricier.... but then I'm worth it.... besides I figure that if I carry minimal gear I want the best, most optimal, most versitile gear.
I would add to last nights post, that a major infuence in our movement to under quilts was Ed Speers true pioneering development of the Pea Pod... He proved external insulation was the most viable solution IMHO....They just didn't work for the HHs... Also we wanted to reduce weight by only insulating that portion of the hammock where we lay.
JJ's comment on the Exped air matress is also instructive.... We did not test these in the early days as they did not exist then and the Big Agnes DAMS we largely unknown, though around... these do work for many folk...besides the surface material, the minor lateral ridge groves help in the back venting issue...They do maintain a go to ground capability for those that want to retain that capability, for whatever reason....They do raise the center of gravity, which can be a stability detractor in narrower hammocks (ex. M1965 commercial copies, travelpod, mosquito and home mades of the 40-50 inch wide range)... though lighter than the wide, thick inflatables they are still relatively heavy... they are still taking space, requiring placement and not as luxurious as the hammock material alone....but they do get a Go.