Loc: Kitsap Peninsula, WA
I usually use a thin plastic painter's tarp for a ground cloth under my tarp. It has always worked fine, but I think I could save a little weight by simply using one of those Space Blankets I see advertised on Ebay for a buck. I was wondering if anyone has done that. I know they wouldn't last long. The plastic I use has lots of duck tape patches and isn't vary durable either.
I used an e-blanket, though it was far more than a dollar, as a ground cloth on some desert backpacks. It served a second purpose as a sun shield, as my wife doesn't fare well with heat at times. It acquired lots of rips quickly. I've had better luck with crossed linked polyethylene , sold as polycryo, or patio door insulation. You need the 1.5 mil, not the .75. This is pretty durable and a few ounces for a solo groundsheet. I'm guessing the dollar stuff is meant for one use and would be in the trash very quickly.
My buddy uses one as a ground cloth under his tent. It is difficult to work with because it is so light and flimsy. He usually shreds his setting it up and it never lasts more than one set-up. Its always seemed like a really waste to me.
Loc: Eastern MA, USA
This may be another YMMV situation. I use a mylar blanket slung under my hammock. Yes, it is noisy, but one can last me all season and beyond. Also, I just returned from a trip to FL. On my bucket list was camping at a waterfront site in Fort DeSoto (County) Park. I used a space blanket under my <$20 (well-known bidding site) tent. The base was mostly sand with some small shells. Even with moving the tent, between sites, the space blanket looked pristine when I put it away. No, it did not fold as small, but it at least was the same weight.
That said, if you have the opportunity to use Polycro, my opinion is "Go for it," unless you are in a sun-baked situation. I also used a one of these blanket under my tent in the Grand Canyon some years ago. With afternoon temps reaching 120 F, the ground didn't cool much before about 1 AM. The first night, the heat was somewhat reflected away from me, the second night (not moving the tent) the ground hadn't heated under the tent.
In windy conditions, you may find it easier to spread the lightweight blanket after erecting the tent, then working the blanket under it.
Too crinkly and they shred. I will use space blankets for the underside of my hammock to block wind. The reflective nature is overrated. Tyvek....any Tyvek works well for me. Homewrap, kite tyvek, anything you can get your hands on works. A sheet of silnylon also works well and I think that's what's in my pack now, for tarping. Coated ripstop works fine too but is a tad heavier than the above choices.
Loc: Eastern MA, USA
You might also show your students how well the blanket works as a sun shield. I forgot to mention earlier that we found one of these set up with hiking poles, etc., worked well as a temporary shade/shield as we took a break along a sun baked trail. A friend set one up behind us to reflect the heat from a campfire as well as block wind from that side on a very cold night. Think variation of a reflector fire.
A word of warning. I had a space blanket in my backpack unused for several months and when I took it out it disintegrated. They do have a shelf life so might be wise to replace occasionally. Agree with other that they will tear pretty easily and not meant for prolonged use.
I'm a polycryo fan as well (I use the heavy duty window covering which someone else mentions). Because it blows away so easily, put small pieces of gorilla tape at each corner, then added grommets. I can stake down the polycryo so it doesn't blow away, and then set up my shelter. I can then remove the stakes from the polycryo if I wish. Works like a charm, and has lasted for a couple of backpacking seasons so far.
I too found a piece of thick painters tarp to be adequate.
I found that if I put in INSIDE the tent under my bag, it was a fine vapor barrier but if you put it under the tent it funneled water under and you get MORE WET. We have demonstrated this often, try it yourself if you wanna get wet put the barrier under the tent. Space blankets are a waste. I want gear that can be used over and over. Jim
These are my own opinions based on wisdom earned through many wrong decisions. Your mileage may vary.