OK, this is scary. I, too, have been recently playing round trying to come up with an alternative to the bulbous sleeping bag.
I have a US poncho and poncho liner (I have the German flectarn versions, too), which work OK in temps between 40 and 65 degrees F. Advantages are that the liner is compressible (fits in a butt back with room to spare), and dries easily when wet. Disadvantages are that it is too hot above about 65F, and not warm enough under about 40F-45F. Adding the poncho gives you a few degrees more comfort, but only a few. And, in warmer weather, adding the poncho for rain protection makes the combo a sauna. There are Thinsulate poncho liners on the market (
Brigade Quartermasters ), but they are pricey, and some reviewers claim they are not all that much warmer.
I still like the flexibility of the poncho-as-bivy-sack approach, so I started experimenting - not with eliminating the poncho/poncho liner, but trying to enhance it. I've tried two options recently: First - adding a thin wool blanket in between the poncho liner and the poncho, and second - adding another poncho liner. Using Cliff's "Am-I-Still-Warm-with-just-a-T-Shirt-after-an-Hour?" Test (utterly un-scientific) and several recent 27 degree nights (yes, we have those down here...), here are my findings:
Poncho/wool blanket/poncho liner combo: Very toasty. Could have used it all night and, I suspect, at lower temps, too. I selected wool since it will keep a lot of it's insulating ability even when wet. My modifications to the wool blanket are to add small grommets to match the grommets on the poncho, enabling you to run the strings of the poncho liner through the blanket grommets before tying the liner to the poncho. Keeps the blanket (somewhat) in place. Down sides: Wool blanket/poncho liner are not a compact item when packed. About 1.25 times the capacity of a US butt pack. And heavy, too. About 5lbs., total.
Two poncho liner combo: Toasty, but not as much as the wool blanket combo. Had some cold spots where elbows, knees and shoulders pressed the liners too thin. Again, I could have used it all night. Down sides: Bulky as all get out, but highly compressible. Using the Grunt "Stuff-and-Smash" method, you can - just - get two poncho liners into a US butt pack. I'd be worried about loss of loft/insulating ability being so compressed over time. The combo is lighter than the wool blanket one, though.
Other issues: Both options rely on the poncho snaps for closure. Great, if you have to jump out of your rack quick when the Hottentots begin shelling your position; not so great for keeping in the warmth. Leaves gaps, you see. Would put a zipper on the poncho liner (as per Ranger Rick's mods). Closure of the poncho ends, where there are no snaps: I gather up the ends, garbage bag style, and them tie them off with a bit of para-chord. Works well so far (make sure to leave a bit of the side seam open for venting), though it does make the whole affair look like a large, woodland camo joint (think 70's lingo, folks). Thought of calling it the "Cheech and Chong Sleep System"... <img src="images/graemlins/grin.gif" alt="" />
Any thoughts would be most welcome.
.....CLIFF