Quick question on Polycro ground sheet…

[jimmy b]

Hey folks, first nights out with our new Duplex this weekend and we will be using a polycro ground cloth. As this stuff shrinks with heat should I lay it in the sun before cutting the piece I need from the field or won’t it shrink with that kind of heat?

Thanks all, and for those that would say don’t bother with a ground cloth…I hear ya.        jimmyb

[Lester Moore]

You probably need more heat than standard outdoor temps to shrink polycro. I’ve had no issues with it shrinking up to the low 80’s in the sun drying out. As for using a ground cloth, why not? Polycro is light, keeps sap off of the bottom of your tent, provides a modicum of puncture protection and plenty of abrasion protection – and it’s a nice thing to take a nap on or lay your pack on during rest stops along the trail.

[Greg Deitrick]

I’m a noob and no ground cloth sounds crazy to me.

I haven’t used polycryo out in the field yet, but back in the day I put it on windows and shrank it with a hair dryer.  I just checked; on low my hair dryer puts out air above 120 F.

I’m doing a test in the driveway now.  I expect temperatures above 95 F before too long.  Maybe up to 100 in direct sun.

[Greg Deitrick]

My thermometer is reading 109 F on my driveway (full sun). No significant change in size.

It seems to me that this stuff should be great for ground cloths, ponchos, and stuff sacks. These are not high stress applications and I don’t see that cuben offers much advantage. Double sided tape for seams and single sided tape for reinforcements and I would think most people would get a very good service life for a low investment in money and time.

[Greg Deitrick]

I got no shrinkage with temperatures up to 110 F. The material was laying on concrete in bright sun for maybe 1/2 hour.

I got shrinkage of 2.3% in one direction and 4.4% in the other direction after exposing to temperatures that ranged from 110 F up to over 120 F (maybe 138 F). The material was wrapped in a black plastic garbage bag and placed on my driveway. It was partly cloudy. When the sun was behind a cloud the temperature was 110 F; when the sunlight was bright the temperature rose to 120 F or more. When I went out the last time the thermometer display wasn’t working properly; I think it read 138 F, but it didn’t start working properly until the thermometer cooled off a bit.

Outside temperature in the shade: 93 F.

[David Thomas]

Another un-named (because he lives in CA, married to a vegetarian) BPLer and I managed to wear through a poly-cro groundsheet by butchering a bear on a crushed gravel surface. Those rocks were sharp and pointy and the three of us (me, him, and the bear) were 650 pounds pulling and tugging on that sheet as we wrestled the carcass around many times.

All in all, a pretty extreme use and the poly-cro lasted fine for most of it. And, of course, was super light and compact to haul in and out.

[Jo P.]

I did manage to shrink my polycro ground sheet by leaving it in a hot car. I don’t know the actual dimensions of the shrinkage, but it was severe enough that I had to toss it. I still like the material, though.

[Diane “Piper” Soini]

I wouldn’t worry about the shrinkage. I’d worry about people wrestling dead bears on it though.

[Todd T]

Don’t y’all know why they put floors on tents?

[jimmy b]

Thanks very much to all. I ended up laying it out on the hot driveway and I think it lost an inch or so but as its kinda stretchy (at least when warm) its hard to tell.

Dave-  Geez, can’t imagine a better advertisement for the product than that! Maybe you can work an endorsement deal.

Oh and Todd…..”we here ya”  :)

[Michael Sirofchuck]

Polycro under floor is the way to go – virtually weightless and protects the floor.  Yes, Tod, we all know why they make tents with floors; the point is do you want the abrasion, dirt, punctures in the floor or a SUL groundsheet that is easily replaced?  Having paid a lot of money for my Duplex, I want the sucker to last as long as possible and so employ a little bit of insurance with my polycro groundsheet.

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