I will be trying a new sleep system this year, using VBL technology.
Here's the idea from inside-to-outside:
1) Close fitting polyester wicking thin base layer.
2) VBL "Sauna Suit" vapor barrier top/pants with elastic cuffs.
3) Sleeping bag.
4) Outer "bivy" made from AMK emergency "space blanket" bag(thin reflective mylar).
5) Neo-Air All-Season R4.9 pad.
Here's the concept:
1) Base layer creates "micro-climate" inside VBL suit.
2) VBL suit reflects body heat and traps moisture inside, to prevent down degradation in the sleeping bag. Also serves as a liner to keep the bag in good condition.
5) Sleeping bag provides the insulation layer.
6) The outer "space bag" bivy is waterproof and windproof, and can be used when the inner VBL suit is being used. Thermal reflection of heat back into bag, and wind-protection, and waterproof shell.
7) This "should" provide a fully dry and water-protected down bag from inside and outside, while the dry body heat pumps the down to maximum loft, providing best warmth.
8) Neo-Air All-Season Pad handles the underneath duties.
Now, "THE QUESTION"...
How do I pick a bag rating for a system like this?
Since the VBL and outer are likely to add a fair amount of warmth to the system, do I buy a bag rated for the temp range I expect to see, or do I buy a lighter-weight bag and bank on the VBL and "space bivy" system to push the rating of the lighter bag?
I have some speculation that it could do this, but I'm asking for opinions and experiences.
What are the suitable ways to regulate temp if it gets too hot, but the outdoor temps are below freezing?
I'm looking to use the most advanced technology available for this type of system, and I have read Skurka's page on it, and it seems that layering and venting is important for activities with VBL, but what about just sleeping?
If necessary, I CAN layer bag warmth, because I have a MontBell Thermal Sheet with 1.5" down loft, which I could put inside or outside the main sleeping bag for layering functions, depending on what sleeping bag I choose for the system.
There's just alot of "gray area" around this subject, so I'm asking about it.
Thanks in advance!