Polycro Tarp Tested!

[Gregory Petliski]

"Interestingly, I just searched and it seems that polycryo is slang for CLP solely within the BPing community (originating from Gossamer Gear, of course). I found no other references. Ironically, the URL for the GG webpage uses polycro."

What does CLP stand for? I too could not find Polycryo outside of Gossamer Gear, whats it called if you went to a hardware store?

[Franco Darioli]

http://www.acehardware.com/family/index.jsp?categoryId=1259828

[Michael Ray]

CLP is my abbreviation for cross-linked polyolefin, which is what this stuff is though there are MANY varieties of that as well. That makes me wonder how different it may be between brands.

Polycryo seems to be a word Gossamer Gear made up.

Window shrink film or window insulation kits are what you would commonly find it as. So the southerners will need to order it most likely.

[Bob Gross]

Some of you materials scientists out there ought to give us a list of these modern materials with chemical name, common name, and relative advantages or disadvantages of each, maybe something like "tougher than generic polyethylene," other names.

Start with:
Cross-linked polyolefin, Polycryo, …
… Dyneema…

Thanks.

–B.G.–

[drowning in spam]

Yep, I couldn't find it at my local hardware super store.

[Michael Ray]

Yeah, I can't imagine window insulation would be high demand in SoCal. :) There are a variety of kits in a variety of sizes that you can order – 3M, Ace, Frost King, Duck, … (5000+ hits in Google Shopping)

[will sawyer]

Hi Dan,

I'm making a very similar tarp (nearly identical) and I'm wondering how you attached the ridgeline to the tarp at the edges (or if you did at all). I am planning on tying on a very small loop to the tarp and then using a friction knot on the loop to grab the ridgeline cord. Also, a big thanks for all the testing you have done, it has been a huge help with my project.

[Dan Johnson]

Will

I'm stoked that you're building a tarp too! For my ridge line I simply ran the cord under the tarp. For the ridge line tieouts I made a small hole (just like the rest) so that I could run the cord thru it. This I thought was definitely needed since I was affraid that the isolated stress from the cord would tear the Polycryo fairly easily. Because the cord had to go thru the hole in the tieout it rested the cord stress on the burly Gorilla tape. After building it and setting it up I wish I would have added ridge line tensioners to tighten the material along the ridge.

And of course we'd all like to see pics! Plus if you could weigh your tarp for us that'd be sweet. I can't find time to find a scale to use or else I'd weigh mine :(

Also what size is yours?

[will sawyer]

I think the tensioners will help a lot, I have it set up inside to test (strung between two posts of a bed), and with a bit of tension across the tarp there is little stress between tarp and guyline, except at the reinforced edges.

I used a 84" by 110" sheet, is was labeled for 'outdoor use' and cost a dollar extra. It also did not include the hairdryer shrinking in the instructions. Either they expect UV from the sun to shrink it on windows, or this might be a non-shrinking version. I 'hemmed' all the edges with the included double sided tape and used gorilla tape for the guyline attachments (total of 12: ridgeline, four corners, three on each long side).

[Dennis Park]

any updates on the research or photos of newly made poly tarps?

[Dan Johnson]

@Dennis

So far mine is holding up nicely so nicely I haven't needed to make another. My site selection techniques have improved drastically since using this material but it's paid back more so in it's low cost and low weight. I have been thinking of making a 6×8 for more "emergency" situations though.

[Chris Martin]

Did this yesterday as my first MYOG project. Hemming the edges was very finicky; toward the end I found that it's much easier if you tape down the whole tarp taut first.

My tie-outs are gorilla tape wrapped around heat shrink tubing. I didn't read the thread recommending nylon washers until later. Fortunately, the $7 window insulation kit included enough polycryo for me to make another one!

[Dan Johnson]

Lookin' good Chris! What size did you make?

[Chris Martin]

The kit came with a 62" by 210" sheet, so I cut that in half to make a 62" by 105" tarp. I'm considering the first one just as practice. Now that I know how to make neater hems, and found the thread suggesting nylon washers as grommets, I plan to use the other half to make a better tarp with more tie-outs.

The hardest part is just keeping the cat away while I work with crinkly plastic and string, essentially her two favorite toys.

[Michael Ray]

So after over a year of waiting, I finally decided to pull out one of my large pieces of polycryo/cross-linked polyolefin (aka window shrink film) and make "Prototype 2" of my half pyramid. I wasn't able to pull it off in time for my recent trip with my boys, but I have Scout training this weekend with some good storms and winds in the forecast.

I had already had in mind a few design changes and I incorporated others from Dan's research and threads the past couple months – using the supplied double-sided tape to "hem" the edges and nylon washers instead of loops of tape for my tieouts. So here is the first pitch as barebones as it gets.

I bought a pack of 50 nylon washers at Fastenal for $2. They were too small for my trekking pole tip at the peak so I just used a metal washer I had. Detail of the pole connection.

Cross-linked polyolefin is known for being tricky to adhere to and I can tell the weatherproof adhesive on the 3M 2120 tape does not stick as well to it as it did to the LDPE so I used more tape than I would have otherwise. That may also make adding netting without sewing a challenge if I do that again. Here is a view with a full-size pad in it, where I'm playing around with differing peak heights and how far out the sides are pulled.
It took about 3 hours, which included cutting the size down to 6' x 9', taping all edges, taping the 2 ridges, adding all the tieouts and running to the store for washers.

There are a few things I'm still not decided on yet.
1. Adding shockcord loops to some or all 4 corners as I did on #1. This material isn't as stretchy as LDPE so it takes much more force to deform (though I had reinforced the LDPE with tape pretty well). My gut tells me it should be fine without them.
2. Adding tape down the center. I was forced to on #1 since that was a seam, but it did seem to keep the pitch tauter. The LDPE would deflect a fair bit in the wind. I may compromise and add a tieout a couple feet up from the edge.
3. I may add a bit more tape on some tieouts as I get a better feel for how the forces act on the material. For now I distribute the load perpendicular to the "ideal" force, but I've already seen where I don't always pull the front corners from close to 45 degrees. I may also need to change to the Gorilla Glue tape if 2120 does not hold long term.
4. Put the pole washer just a wee bit farther out from the edge so it's not on as much an angle.

Specs: 6' x 9' (finished size about 1" shorter because of the "hem"), total weight with the tieouts and washers but without guylines – 150 g (5.3 oz). FYI, the tieout tape and washers (9 plastic and 1 metal) added 22 g.

Thoughts on improvements?

[Ultra Magnus]

I think that's a pretty impressive weight for such an inexpensive shelter.

Have any of you guys tested these shelters in any kind of significant wind? Could they stand up to some 30mph gusts? How long could it hold up to strong winds w/o failing?

BM

[Michael Ray]

My LDPE version has seen 30-35 mph gusts. I'd expect it to be noisy but last indefinitely. I'd assume the same performance from this material. We were supposed to have 35 mph gusts at training but they just say winds up to 20 mph and not as much rain now. Bummer.

[todd]

Cool shelter Michael!

I'm gonna build mine soon. These are awesome.

[Dennis Park]

Could you add a photo on how you taped the tie outs along the sides? (I guess this request would apply to all of you who have made a poly tarp.) I'm trying to figure out if the washer has to be taped off of the poly as in the photos from the poly testing thread or can the washer be placed on the poly and then taped into place. Thanks.

[Dan Johnson]

@ Dennis:

You might be able to get away with putting the washer on the Material itself and then taping it down. The biggest worry I see is that the material is not very tear resistant (non at all really) so once it has a hole it is so much more susceptible to complete failure.

I recently got a new job (yay for me!) and i now have access to a scale. Today at work I weighed my Polycryo tarp and it came to 10.8oz. And that is with a crap load of heavy cordage and excessive tape used on all the tieouts. Also it is 7'x9 in size. I have no doubt that my next one (which will be smaller in size) will be sub 6oz if not less.

[Dennis Park]

Very nice! Keep us posted on your next model. Close ups of the key points and weights are always appreciated.

[Michael Ray]

Dennis,
I think you could do it either way. It would be a little cleaner putting them within the hem, but I would still add tape in both directions. I don't think the material would continue to tear because of the tape but that would be a good test for you to do. :)

FYI, I have one long piece of tape, containing the washer, that runs parallel to the ideal force direction, looping from the top of the material to the bottom of it. The "loop" is either an 8" piece for corners or 5" piece for secondary points. Then I added 2 perpendicular pieces on the top and 1 on the bottom. I used only 1 on the top in general for the LDPE version but the 2120 doesn't stick as well to this material so I thought the 2 extra pieces were good measure.

I just went out and took these before the sun rose. I found it interesting that ALL the places where there was tape had a film of condensation. You can see where I wiped the hem in this pic. You can also see I'm not pulling at exactly 45 so I made add a couple other pieces of tape to distribute the force better.

Here is a side tieout. It's also the only place on my "hem" I had a major wrinkle. This was the last side I had done so it wasn't taped down at all (I removed the tape holding the corners down tot he floor as I went). I was also going too fast. :) It's a bit easier if you can keep the material taut.

And here is the only other condensation. Granted it didn't have my respiration to deal with but it also had no groundcloth and the back is essentially pitched to the ground.

Dan,
I'm surprised your's is that heavy. You must be including guylines and stakes?

[Dan Johnson]

@ Michael

Being this was my first tarp I experimented with I used a "butt load" of tape. And it doesn't help any that the Gorilla Tape that I used is insanely heavy. Not to mention that because of all the "over engineered" guy-outs I made it doesn't pack up very small due to the tape not folding very well. My packed size for the tarp and guy lines is the size of a nalgene. And my 10.8 finished weight does include the guylines. I'm using cheap cordage from REI that is pretty thick/bulky/heavy so I'm sure that's not helping me.

My overall weight for my 7×9 tarp, guylines, stakes, and ground cloth come in at 20oz. Keep in mind I'm not useing the lightest stakes either.

[Michael Ray]

It didn't look like you had used more than 1 large piece per tieout. As long as your guys are, I bet they're at least as heavy as the tape. Anyway, for reference, my Prototype 1 (LDPE) weighed 21.8 oz with everything, incl netting W/ zipper, ground cloth and stuff sack. That was a 6' x 8'.

I'm not sure I'll like trying to sleep with a headnet (or just a hat for that matter). I really liked taunting the skeeters in Wind Rivers through my netting. :) Keeping the annoying buzz away from the ears may be worth the weight penalty to me, but I'll give it a go without for a while.

[Michael Ray]

I actually had a failure point this morning. One of the washers ripped out of the tape (the very corner I took the picture of earlier). I did get pretty small washers (3/8 OD I think) but this tape has worked well for me in the past. Now I know I must add another layer of 2120 tape around the washer. You might not have this issue with GG – just something to watch.

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