In The Complete Walker IV, Chip Rawlins writes about using a VBL half-sac, covering from his feet to his upper chest. According to Rawlins, it was made by Moonstone but is no longer available. It had an elastic band at the opening. He takes this to bed with him, and if he gets cold, he pulls on the VBL half-sac.

Has anyone tried this type of VBL method? Rawlins suggests that it extends the temperature rating of his sleeping bag from 10 to 20 degrees.

Craig,

I have used this method with the new heatsheets bivy sold here at BPL. I agree with around 8-10* of extra warmth. I am a cold sleeper though, so YMMV at around 10-20*. Of course you get the main function of the vb which is to keep your insulation from degrading due to moisture build-up from passive persperation.

I recommend sleeping in only a thin silkweight layer as the parts of your body in the vb will be in contact with moisture. You probably know all that stuff though.

The heatsheet does not have an elastic band, but I twist the extra girth into a loose rattail and then tuck it under the part of the bivy at my chest.

I think it is a great idea for preventing most moisture from getting into your bag and, on a short trip, a safety item.