>My concern with any close-celled foam pad, even one as thin as 1/4", would be that it wouldn't consistently form-fit to the hammock, thus creating gaps and cold spots.
The 1/4" does form-fit a bit better than a 3/8" pad, but it is still a bit gappy underneath. Thus, while thicker than the GG ThinLight 1/8", I'm not sure it's actually any warmer in practice. It is better for ground sleeping, which is why I chose it. I think I'll probably be using the GG ThinLight 1/8" and JRB Weather Shield bottom cover more than the HH underpad/undercover in the future, because my few experiments so far show them to be about equivalent in warmth and the GG/JRB combo is both lighter and dual-use (although not comfortably).
I do have an OR Exped DownMat 7 Short, which works very well with my GG ThinLight 1/8" for ground sleeping. I haven't used it under my hammock yet.