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!

Edited by towaly on 09/12/2011 06:21:09 MDT.

Are the type of person that needs:
a 0 bag in -20F weather
a -20F bag in -20F weather
a -40F bag in -20F weather

I just started winter backpacking and vbl last winter so I am still trying to dial my sleep system in as well. I am going to try something very similar to you this winter and I expect my 5F bag to work down to about -15F and then I will be able to sleep in my down jacket and soon to have down pants down to about -20 or -25F. I am a very warm sleeper though. Last winter I was comfortable or slightly chilly to about -10 or -12F in a VBL bag liner and 5F Western Mountaineering bag.

I'm sort of on the cold sleeper side, especially my feet get cold easily.
I wouldn't say that I'm extremely cold sleeping, but I tend in that direction.

I'm thinking that if I can push my bag rating down by 15 degrees using this stuff, it can make it worth carrying it. Plus, keep the bag and down in top shape, without big concerns about wetted bag from either outside or inside.

I am attracted the the concept of this VBL stuff. It seems to make alot of sense, and seems worth working out a system for it.

Edited by towaly on 09/12/2011 11:13:59 MDT.

You just have to try it for yourself. That's the big thing. Bodies are different.

I have an M55 bivy that adds 5-10º without other shelter. My rain jacket adds about 5º and comes more effective in colder weather.

The big thing really is discovering how YOUR BODY reacts.

By what you just said, I think I said how I sleep wrong, I am a warm sleeper. I can take a bag easily 10 degrees colder than its recommended temperature rating.

Based on my last winters experience I think your estimate of 15 degrees is possible. The nice thing about the VBl clothing option is that if you are cold you can put on extra clothing to warm up without the fear of wetting it out while you sleep. The one thing you have to be conscious of is that you don't compress the sleeping bag with extra clothes on the inside or the overbag bivy on the outside. My sleep system is going to consit of VBL clothing as my base, then my regular daytime thermals next. Those two layers won't come off until the end of the trip, then I have my down jacket and pants that can come next if the low temps require. Then the sleeping bag, and last my bivy. I use a GoLite SL2 floorless shelter for my tent, that is the only reason I use the bivy.

I tried a vbl bag liner (metallic fabric emergency bivy)last winter. I really didn't like how the material felt on my body or all the noise it made when I rolled around. That is why this winter I am going to try the clothing.

I just bought a Gold's Gym plastic work-out suit for 8 bucks at WalMart, and it's completely waterproof and has elastic cuffs, waist, and neck. I'll wear it over my polyester base layer. Cheap!
I bought a women's vinyl shower cap with elastic headband for about $1.25 too. It will go under my skull-cap.
I got some large nitrile exam gloves for 97 cents for 8 pairs.
I need to figure out some cheap useful foot covers.

So far, I have about 12 bucks in the whole VBL experiment. Fairly lightweight too.

I'll go down to my local hiking shop tomorrow to get a AMK "space bag" for my outer bivy. They were closed today. That should only cost about 8 bucks, and I'll cut it and make a veloro closure on the side so it's easier to get out.

Edited by towaly on 09/12/2011 11:39:54 MDT.

bread or newspaper bags.

For your feet try bread bags. You can go to a local bakery and ask them for a few dozen they will look at you funny but if you buy bread in one of them they some how will just end up in your bag. Normally people use 2 per foot per day. I found that I could do 1 per foot and get 1-2 days out of each pair before a hole riped in it. Excellent for testing the system. I don't like the feeling on my feet, but that could be an issue of my boots are getting old and a little bit loose so the bag helped them slide.

use seal skin socks, yes they are heavy but they can also be used with a liner sock and trail runners (1/2 to full size bigger than without those huge socks) for your daily activities. I love them for winter use with my regular trail shoes. they are said to breathe but i think it is so little that they will work like VB socks but also add warmth.

-Tim