I live in an earthquake zone. In fact they’ve been threatening us with “The Big One” since I can remember. Had a couple fair shakes too. Anyway, I usually have a few survival type items kicking around in my backpack. When I worked across a major river from home, it seemed like a good idea and I just kept 'em.
This being the Wet Coast, naturally I have a rain poncho. It’s a pretty good one. It’s actually two layers of cloth. The material is a very slick, shiny nylon. (Green one side, blue the other, reversable, if you’re interested.)
I keep one of those foil emergency blankets in my little kit. It’s kind of krinkly, so I figured it would be better, if I ever had to, to wrap myself in the poncho first and then the foil. I’m thinking of getting a few of those stick-on Velcro dots which I’d keep with the foil and not put on the poncho unless I had to.
Now, I assume the manufacturares of the blankets figure you’d be keeping your clothes on anyway and factor that into the effectiveness. I’m just wondering if actually lining the foil would make it useless? Since the nylon is fairly thick, would it make it too effective and overheat me? I know I’d have a problem with moisture.
By the way, I also have a sheet of plastic so I don’t actually need the poncho for shelter.
No; it won’t make it useless; the foil blankets work by reflecting heat back at you that you are losing by radiation (as well as trapping a layer of still air); any heat that isn’t radiated right through your clothes, you needn’t worry about because it will be trapped in your clothing and still be keeping you warm; that which makes it through will be reflected back and either reabsorbed by your body or clothing, again, keeping you warmer.
In fact there are products that contain shredded metallised mylar inside the padding (i.e. between two knitted or woven layers), for reflective insulation.
You probably don’t want to actually sew it in though, because that will limit the different configurations in which it can be used.
About not actually sewing it in, yeah, that’s why I was thinking the Velcro spots would work. If I put a line of them, say every foot or so, on the edge of the poncho it would just keep the foil from sliding off without wrecking the poncho permanantly.
Hey, why don’t they just make sleeping bags with a foil liner? In theory, you could get away with a very thin layer of cloth and it would weigh practically nothing. Is it the moisture retention thing?
Probably; I think some of the ultra-compact all-season sleeping bags (the sort that mountaineers use) do contain some kind of metallised reflective filling, but it would certainly have to be breathable/ventilated, or you’d just wake up in a wet plastic bag in the morning.
There’s also the noise thing. I got the chance to use a mylar blanket for its intended purpose one November evening when a hike ran a bit long and we ended up doing some impromptu camping on the cold dark mountainside. The blankets do keep the cold air out, but they also serve a secondary purpose – the hideous crinkling of mylar will also keep any prey animals far, far away. It will also keep any possibility of sleep far, far away. (The manufacturers of the blanket I was using also cunningly engineered its dimensions so that no matter how you wrapped it around yourself, there was always just enough of a gap to allow in a draft.)
