convert NF propel bag

a smaller volume of air around your body equals a smaller mass of air. it’s easier for your body to heat a smaller mass of air, so it warms up faster. for example, how fast does your body heat a cold bedroom? now,…how fast does your body warm up the smaller amount of air trapped under the covers on your bed? that’s pretty much the idea behind it. to put it another way, is it faster to heat half a kettle of cool tap water for tea, or a full kettle of cool tap water? with all other factors being equal, it’s always easier to heat a smaller mass of anything than a larger mass of the same thing.

however, in the case of the sleeping bag, don’t carry this to an unwarranted extreme. it is trapped air in the insulation and between your body and the inside of the sleeping bag which contributes to its warmth. i don’t believe the bag would be as warm if all of the air trapped between your body and the inside of the bag was removed.

at this point i’ll stop and let someone who understands the principles of heat transfer better than i do take over.

thanks paul. that helps. now i’m wondering if i need to shorten the Propel bag i ordered. (the long was 20 bucks cheaper!) i’m going to be doing some sewing anyway (see my new thread in G-spot).

i’m trying to engineer uh, basically it’s a mini-tent structure. the hard part is the concept of keeping a “door” open so the little guys can find their way in again, once they get through barking at every sound. the idea is that the structure would be kept together by fabric sleeves, much like a tent, but the “sleeping bag” would hang loosely from the structure, providing a cozy vestibule.

if i mimicked the design of say one of those big heavy “clip flashlight three pole tents” but had the sleeping bag hang (from grosgrain) taut at the door and loosely elsewhere?

i have these incredibly flexible light plastic dowels to work with…can a freestanding tent just have two poles? if the fabric sleeves are boss? hmm…tough to visualize the pulling…

I’ve been thinking about doing this same thing. The main thing is as you say

“keeping a “door” open so the little guys can find their way in again, once they get through barking at every sound”

Other than the door aspect, the project is fairly easy. Where did you get the dowels?

i went to the auto parts store, got some very flimsy sun shades. at first i was just thinking about a ring for the door, but since then, i’ve been musing on how to keep it “open”.

if i just make a prototype from fabric, once i have the shape, i can always follow it up with the actual quantum/polarguard delta material. when finished it should weigh no more than a few ounces.

> “shorter”
you’re right. shorten it, but make sure to leave enough wiggle room for your toes/feet to extend & flex. if they compress the bag’s insulation, then you’ll loose some “warmth” in the foot end.

Doggie Shelter:
How ’bout a lt. wt. “doggie” door approach. Free on 3 sides and attached at the top? Dogs (and cats) learn to go through these at home. Just a heavy wt fabric “hanging” door. I did this once on an outdoor dog house. Dogs had no trouble figuring out how to get in out of the cold. For your purposes something like a wire (#10 gauge like used bivy sacks to hold the fabric/mesh off of the face, or a clothes hanger) would form the frame on which to hang the fabric door. It’s flexible & so can be bent to pack & reformed when pitching. The wire might only be appropirate if the dogs are small.

Make sure to use one 90deg turn after passing through the door and before entering the main sleeping area. This is to reduce slightly the entrance of cold air. Better would be a full igloo still entrance like that used by “Eskimos”, but this poses more problems and site preparation when pitching.

How’s that for another suggestion from “Bad Ideas R Us”.

What about the issue of the dog’s exhaled breath – all night in the shelter. It’s got to get pretty damp/soggy in there by morning, right? Maybe I’m missing the picture, here.

(Fornshell-san, where are you when I need you??? Help!!! Any good ideas? I’m sure that you do!! :)