Polycryo Strength Analysis

[Dan Johnson]

Just in case anyone wants to know, I found that target was selling patio door insulation kits for only $2.98 in their clearance section. It's now even cheaper to build something out of this stuff!!! I bought a couple just cause I couldn't say no to the price :)

[Michael Ray]

That's even better than the $4.50 clearance ones I got at Walmart last spring!

[Here There]

A quick note for anyone attempting one of these, make sure the washers you use are robust enough. I was going to use pieces of a milk jug since that's what I had on hand, but in testing some tieouts under repeated stress the cord cut through the milk jug washers and gorilla tape.

In short, use tougher plastic or the store bought washers.

-David

[Steve B]

Anyone have any pictures of a tarp from polycryo? Size of tarp and weight?

Steve

[Michael Ray]

Searching does wonders

[Steve B]

Thanks!! I'll be sure to search before any reply in the future!

Steve

[robert van putten]

"Note that the standard Polycryo thickness is 12 microns = 0.000472440945 inches"

Wait..What?

Where the heck does this "standard" come from??

.47 mils is standard?
Seems like extra thin stuff to me.

Dennis brand window kits say .6 mils for the interior stuff ( 15.24 microns ) and 1.2 mils for exterior film ( 30.48 microns ).

I can't tell how thick the Frost King kits are, but have found one reference on their web site that mentions outdoor kits with 1.25 mil ( 31.75 micron )film.

Dan Johnson, what source are you using for the stuff you are testing, and what is everyone building their tarps from, the thin indoor kits or the possibly twice as thick outdoor kits?

( Edited because I got my darn decimal point in the wrong spot)!

[Dan Johnson]

I'm using the Frost King Interior large patio door kit.

[robert van putten]

I'm surprised!
The thin interior stuff is stronger than I figured it would be.
I can't help but wonder how strong the probably-twice-as-thick exterior kits are.

[Paiolo Montanel]

After reading this (interesting!) thread, I've made some other tests on tie-outs strength.

Using 1" gorilla tape, I've had little success making washer-like reinforcements: I tryed using bottle-PET for building the reinforcement but they broke at nearly 7Kg; then I tryed a tie-out made only with gorilla tape (a simple tape-loop, with double tape inside the loop to make it non-sticking) and resisted more than 20Kg! The nice thing is that it is the simplest tie-out to make… So no washers in my future tarp!

I've then tested two different tie-outs types to discover which tie-out <-> film configuration was the strongest one. The idea I wanted to prove is that making "V" shaped tie-out would discharge the stress on a wider film area than a usual linear tie-out using same tape length. These are some photo of my tests:

(on the left a "V" tie-out, a little more "opened" than desired, on the right a usual linear tie-out)

(this is the desired "V" tie-out shape, even if a little short)

Unfortunatly I had no spare polycryo pieces to test it out, so I used some packaging film I've found in my trash and common tape. BTW it seems that "V" shaped tie-out are 1.5x TIMES MORE RESISTENT than linear tie-out without any weight penalty. I think they would also resist better than linear tie-outs when stress is not perfectly perpendicular (but no test have been done on this).

"V" tie-out idea can be applied on both tape-loop and washers-type tie-out.

I'd be very happy if someone in the forum want to verify the result of my test with polycryo. To do the test please use a square piece of polycryo at least 10"x10". Any volunteer? ;-)

[Michael Ray]

Just a guess on my part but I suspect the resistance has much more to do with the fact that the forces are now at an odd angle to the tape instead of perpendicular. Recall that you can easily rip most duct tape width or lengthwise (parallel to the fibers direction). Can't see why it would make much difference on common tape since there's not that much extra width without a pretty wide V.

[Paiolo Montanel]

Hi Michael!

I probably didn't explained well the tests I've done (and just edited the post to make it more clear):

– first test was a cord <-> tie-out test, and I concluded that a tie-out with a tape-loop was stronger than a tie-out with a PET washer, and that was in general a simpler and strong-enough tie-out for my needs.

– second test was a tie-out <-> FILM test, and using a V-shape tie-out helps augmenting border-width between tie-out and film: as this is the breaking-line, augmenting it helps dissipating stress over a larger area. But I tested it over a common nylon film and not over polycryo, so I'd like some confirmations of these tests using the material we really want to use.

But it is right, as you said, that using an odd angle would perhaps also increase cord <-> tie-out resistence when using duck tape tie-outs.

[Michael Ray]

I see. I agree. I use a piece perpendicular to each normal tieout to spread the stress over more of the edge.

[Paiolo Montanel]

That was also my first solution (a tie-out with a "T" or "cross" shape), but when applying a little tension over the tie-out, the perpendicular piece simply flexed, without (apparentily) discharging much from the main piece. Have you tried it?

[David Gardner]

Short sections of carbon fiber tube used where where the tape folds should also work to spread the loads, especially if coupled with the V style tape tie out. Short sections of carbon fiber tubes can be cut from old or cheapo fishing poles or golf drivers from Goodwill.

[Kodiak Firesmith]

So I've read through this thread and a few others – at this point in time, with formulations from certain vendors turning out to just be vinyl, where can one get large dimensions of the real-deal polycryo? I'd like to make a large tarptent with the stuff but don't want to be suckered into buying the wrong brand of window treatment and not get the "real" polycryo.

[Michael Ray]

The patio door kit is the largest I know of (7'x10'). I have also seen rolls but I think they were only 4' wide. If it's the shrink film then it should be the real deal. It may be the outdoor variety is thicker than indoor in general (I personally don't know if that is true or if it matters) but if it is made to shrink with heat then it is polycryo.

The challenge for you I think will be joining pieces. I believe David had some success with that, but it's critical to use the proper tape and I don't believe sewing would be practical in general.

While I like this material and will continue to use it for my solo shelter, I would not bother making a floored shelter with it. I would attempt to make one with perimeter netting again though like my first LDPE one.

[Kodiak Firesmith]

Thanks for the reply – it sounds like I'll be joining multiple sheets of Duck brand 0.7mil soon. It's going to be a floorless A-frame tarp shelter with doors and if I ever use it, it means I made a mistake somewhere – mostly it's just getting packed away in my daypack so I can hunker down if need be.

[Michael Ray]

Then I think you should consider the half pyramid like I make. Perhaps not as roomy as an A frame, but easier to pitch, good in storms and you don't really need a door though I did make one and have used it once when the wind changed direction at night. That was with my first 6×8 LDPE tarp. I've since decided I prefer more room so don't think I'd need a door. I'm pretty sure in one of these threads I posted a pic of my original 6×8 LDPE next to the 7×9 polycryo version.

[David Gardner]

I believe Michael is correct that the largest available retail size of polycryo appears to be 84"' x 120". The best I have found in that size is Duck's outdoor patio door kit, which is twice as thick at 1.5 mils:

Unfortunately, availability of these kits is unreliable. Walmart often carries them at about $13, but right now it's out of stock and the only ones I can find are on Amazon at *$45* per kit. If you can find it when it's in stock, grab as many as you can. Actually, if anyone can find or has some of these kits at a reasonable price I'd love to buy up to 4 kits. Send me a PM please.

I once searched around for bulk polycryo and found, I think on Ali Baba, rolls of 120" wide material with a center fold so 60" wide on the roll. The problem is the shortest roll I could find was 1000' at about $2/ft, which was a total no-go.

The best tape I have found so far is "Tenacious Tape," which has by far the best adhesion and tear resistance and is reasonably light. It's also very cool because it's clear, so you can make an entirely clear tarp. Unfortunately it's $5 for 20 inches which is ridiculously expensive. Making a single 120" long seam costs $30, and 10 tie-outs for an A-frame tarp are another $35. You could do all of that and more with a single role of duct tape for $7-$10, though.

The second best tape I have used is 3M 2245 Heavy Duty All-Weather Duct Tape. 3M rates it as 5 of 6 on its strength and weatherability scales. It's about 50% heavier than Tenacious Tape and only comes in a dark metallic gray color, so it looks like duct tape and rates low on my aesthetics scale, although it does work very well:

The third best tape is 3M Scotch 2120-A Tough Transparent High Performance Duct Tape. 3M rates it as 5 of 6 for strength and 4 of 6 for weatherability. This tape looks pretty cool and hi-tech, but weatherability is obviously more important for a tarp/tent:

News Flash: While researching for this post I just discovered that Gorilla makes "Clear Repair" tape which is described as having an extra thick adhesive layer, crystal clear, won't yellow outdoors, "weatherproof: Water, UV and Temperature Resistant". $7 for 27 feet. The one drawback may be that it is made to be easy to tear by hand, with a "notched edge design" that would be problematic for use on seams and tie-outs. But the edges can easily be trimmed off with a board-mounted utility blade. I have ordered some to try it out and will run some tests to see how it compares to Tenacious Tape and report back. It would be very cool if it works as well as Tenacious Tape:

[Dave Ayers]

3M XL window kit (one source here: http://www.acehardware.com/product/index.jsp?productId=1896771&cp=2568443.2568453.2626341.2627449) is 7' x 19.7'. Duck has one 62" x 420".

[David Gardner]

I like the size! That would solve the labor-intensive and heavy way that I currently fabricate vestibules, and eliminate the seams too:

Now if it only came in 1.5 mil thickness it would be perfect! I'm still going to give it a try though.

[Michael Ray]

I use the Duck patio kit as David described and 2120 tape. I use the Duck window kit mentioned for groundcloths (I've only made 2 s far).

David,
Have you given up on the nylon sail repair tape you'd been using?

[David Gardner]

As much as I prefer the light weight, strength and durability of the sail repair tape, I have found that its adhesion isn't as good. The side tie-outs tend to "creep" and I've had a couple of them just let go. Longer pieces of tape might mitigate the problem, but for my purposes (commercial production) I need things to be as bulletproof as possible. I actually have one full and one 80% roll of blue sail repair tape and two of green, if anyone is interested in trying it out. No charge except shipping cost.

[Kodiak Firesmith]

Thanks a bunch everyone for your responses, such good info.

It's very frustrating that Walmart of all places appears to be the sole supplier of the 1.5 mil kits – I've not spent a dime there in at least 10 years now and don't plan on it either.

Maybe I'll email the Duck people and see if they know of any other suppliers that might just not be on the internet. Hell, maybe one of the Ace managers could be tempted into carrying it, I think there's a local one around here in Pittsburgh.

I'm going to buy the 62×420 inch 0.7mil and maybe experiment with layering for 1.4mil and perhaps enhanced shear resistance. I was already thinking of making a "ripstop" version of this by using tape to make a 12"x12" grid pattern so that failures might not be totally catastrophic and might be somewhat field repairable.

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