US Modular Goretex Sleep Bag System MSS Complete 4 part (Rated -40F)
Product Review (submitted on April 26, 2006):
I slept in mine down to 38 degrees wearing socks and drawers and was warm enough to sleep.
Here's the ratings for the MSS:
Sleeping Bag, Patrol (30 to 50 deg F), MSS Green NSN 8465-01-398-0685
Sleeping Bag, Intermediate (30 to -10 deg F), CW, MSS Black NSN 8465-01-398-0687
Compression Stuff Sack, Black NSN 8465-01-398-5428
Bivy Cover, Woodland Camo, Camo NSN 8465-01-416-8517
Theoretically, the whole shebang is supposed to provide for a minimum of 4 hours sleep at -40.
Usually in the army we just carried the patrol bag and bivy rolled up in our shelter half. The patrol and bivy roll up quite small, it's the intermediate that makes up the bulk. If it was a little chilly for the patrol/bivy combo, we'd use the shelter half as a blanket (I don't remember ever actually assembling it into a tent once I got out of training).
For really cold weather I love the intermediate bag's double thickness at the feet. Sleeping with the whole thing nested, I went down to 9 degrees and was plenty warm.
I'm a hot sleeper, but I seriously doubt the -40 thing, even for me. But for anything but true arctic conditions, I think the MSS is more than adequate. I've noticed that the MSS's bulk always attracts attention, but even bags like the snugpack rated to 0 or below, only compress to about the same size as the MSS. For a do-all, layered system, at the prices they go for, I'd call the MSS a best buy.