Originally Posted by tdickenson
Ive just tried one night at -2°C with the space blanket replaced by a panel of PU coated polyester tent fabric. There was no significant difference in warmth or condensation management, but it was substantially less noisy!
Originally Posted by Owl
Interesting. Wonder if just using a layer of 3mil contractor bag cut open to fit over the underpad would have the same effect?
It is quite possible. I have been asking for years: is the obvious ( to me and at least a few others) benefit of adding the sp.blanket to the HHSS due to radiant block, due to some radiant added to a full VB effect, or is it just all VB effect
? No one has given me a definite answer - or I have forgot if they did - and I have never taken the time to try and rig up some "controlled" comparisons. ( probably because this would be tricky trying to account for all of the variables. )
Here is the problem of trying to test: look at tdickenson's test. Apparently, he was warm enough at just below freezing. Right about where I find a basic system good for for me. Has he been any lower than that when using the SB? Certainly some here have. If he can go lower, is it due to adding some radiant block to the VB effect? But for that matter, could he have gone lower with the PU coated polyester tent fabric, even as low as with the SB?
If you can get say 15F added with a plan VB, can you get maybe 17 or 20 with a radiant + VB? Does any one know? I suspect that most of the effect is VB, but is it all of the effect?
I think if there is any benefit from any radiant block, it is small, but I'm just guessing. It would be hard to determine from back yard tests if your VB got you a 15F boost but the SB got you a 17F boost. It could be found out in some sort of controlled lab test, but a small difference would be hard for me to detect. And a test would have to be side by side on the same day with all other insulation and materials identical. Even then, it would be tough to tell- by feel - a small dif. Maybe if some sort of thermometer was used, taped to your back and transmitting to a separate unit?
Being an on and off VB user for years, it "seems" to me that I notice the warmth boost much more quickly when I add an SB over the HH pad than I do when just using VB clothing. But that could be in my head, and is certainly not an A to B comparison.
Plus, Dirtwheels recently got a warm at 23 night out of a 45F UQ, an extra 22F. That is starting to push the most optimistic claims I normally see for VBs ( an extra 15 to 20?). But it could just be the UQ is good for several more degrees than rated, at least for Dirtwheels.
How about testing with- if there is such a thing - a breathable sb? If it really was quite breathable, and if you still got a significant warmth boost, then I suppose that would mean that radiant block counts for something?
Regardless, interesting discussion!