Quote Originally Posted by oldpappy View Post
Tom's very informative note is very interesting, thank you for pursuing and sharing this.

FYI stuff:
I don't normally have a moisture issue, so to/for me it seems the new 2 layer HHSS system would not be a good fit due to his quiote " We also have had reports that putting the space blanket under the open cell foam pad solved the problem of damp sleeping bag but with less efficient radiation."

I've found by being inside a mummy bag (vs using a TQ) when below about 40F provided me with the most comfort. My SB is synthetic so there is some bottom insulation when compressed as well as radiation heat from the SOL SB I use.

The only moisture issues I have had were 1) a calm cold night at 100% humidity (with ice fog) I had a couple tablespoons of water in the under cover, and 2) I used a GG Closed Cell pad as supplement insulation and the 36X30"CCF pad held the undercover sides open - I was on my side and my breath entered the UC and condensated/froze on the side of the UC = self inflicted issue.

Now I do have a simple mod I am trying this winter with good results so far (only tested for 2 nights so far). I took a large ~18" soft side cooler and disassembled it. The insulation is thin flexible foam with foil on one side - very light. I placed this thin light insulation on top of my OCF pad and under the SB and so far got to 30F = 10F better than my normal 40F comfort range.. I also made a 'kidney pad' from an 18" square and placed it right on my back (elastic on fleece sleep pants holds it in place). This worked great too.

Enough for now, Time to go shovel snow.
You are pretty much where I am with this system. IOW, I never have an issue with damp anything, so I probably don't need the new solution, though it might be just the ticket for some. And who knows, I might even like it better if I tried it. But I am hesitant to give up the protection of the sil-nylon UC if it is not causing me a problem.

And what you said about the CCF pad causing the UC to fit poorly, and then condensation from your breath froze to the side of the UQ( good that it froze rather than running down into the UC?): I can totally see that happening. I can't say I have had it happen, but I have been concerned about just such a possibility. When I was in this system at 6F, and using the over cover, I was glad I used a frost bib. Though I ended up bone dry, without that ( and VB clothing? ) I might have ended up with a lot of condensation(probably, but can't know for sure), maybe even with some of it freezing to the UC/TC or running down the UC into my insulation. Would not surprise me.