What Happens When You Fold Paper A 7th Time?

Ever heard that myth(?) about not being able to fold a sheet of paper more than 7 times? Well if you’ve ever tried it you know it’s impossible to even fold it a sixth time with your bare hands… but what if you have an industrial hydraulic press to help you out?

News to us, a YouTube channel exists called the Hydraulic Press Channel, dedicated to — you guessed it — crushing absolutely anything and everything with the help of a hydraulic press. Narrated by a lovely old chap whose accent (and colorful language) we can’t quite place, the channel is filled with amusing videos of guaranteed destruction — including paper.

But the result is not what you would expect at all — you’ll have to watch the video to see. With a bang and a tremble the seventh fold seems to change the material properties of paper. Can anyone explain what’s going on here?

Glad to know even with Mythbuster’s dead and gone, someone is out there keeping the myth cracking alive!

[via r/videos]

77 thoughts on “What Happens When You Fold Paper A 7th Time?

    1. The bang is actually the product of a cold fusion reaction, It’s surplus energy. If a billboard was folded seven times in a car crusher, it could power a small town for two weeks.

    1. Looking at the final product, I’d go with the folded edge for the last fold bursting.

      Hypothesis: Paper can be very strong in tension, and there was a lot of stored energy in the system when it occurred, due to flex of the press frame/bed. Fracture started, then ran as the speed of sound for the material, taking a few microseconds to travel the 25 or 30mm across the sheet. From the point of view of the press ram and bed, the resistance disappeared, the parts accelerated as a=F/m, and soon after hammered the wad of paper. Hard. Really, really hard.

      1. Sounds reasonable – you don’t normally expect paper to have a brittle fracture, but that seems to be exactly what happened here, followed by the flexed press bed unloading as the paper stack suddenly became a lot thinner and crashing the two sections together.

  1. Paper is mainly cellulose, which is highly compressible. By taking effectively 128 sheets of paper and compressing them together, you are performing a similar operation to the compressive forming of tablets, “Microcrystalline cellulose (MCC) is one of the most important tableting excipients thanks to its outstanding dry binding properties,…” Now paper is not actually microcrystalline cellulose, but it will have similar properties I would imagine.

      1. Remember, this guy is from Finland. They don’t have much else besides rock/metal. It’s not your regular “uuuah, manly metal for my manly video about my manly V8 motor in my manly muscle car on a manly piece of straight asphalt doing manly acceleration to get manly 1/4-mile times. Yeah…uaaah…manly”

  2. By bending it the outer layers of the paper stack get tension the inner ones a compressive stress state and because paper on paper has a relatively high coefficient of friction and it gets pressed from above this stress state cannot be relieved and the outer layers will rupture due to tension => bang.

    The state of the paper stack afterwards could be caused by plasticity over a certain load and hence bonding.

  3. This is a physical constant of the universe, just like the speed of light through space. As you approach the 7th fold, stuff starts getting weird. Although you can never reach full 7th fold it has been possible for researchers to fold paper up to 99.998% to 7. The video shows how it would look like if the paper passed the 7th fold but only to an outside observer. The paper itself has not physically received a 7th fold and the energy collapsed though paper-white radiation leaving nothing but a disc of cellulose plastic that has a total of 0 folds. I know that sounds counter-intuitive but if you operate in areas with such large folds and energies the concepts become hard to understand.

  4. The material just fails because it gets bent/folded to far, because theres so much energy coming from the press, it pops with a loud bang rather then just sheer silently. Or thats my theory anyway

  5. It makes sense, when you compress that cellulose, and most often a good % starch, it first presses into a layered solid bound by the starch and the crushed matted fiber, then suddenly the cellulose fibers let go in a fast cascade as it splats out to the sides.

  6. As a printer, I have come across this phenomenon a few times. When multiple sheets, or wonky screwed up sheets get squished in the metal cylinders they come out powdery and dry.
    It’s like the moisture has been removed and is rock solid. I have seen one sheet of rolled up paper leave a meaty dent in the steel cylinders.
    You wouldn’t think one sheet of paper could stop a press weighing tons, and spinning at 15000sph dead. But it does and with an amighty bang.

    1. As another printer, I can certainly confirm this. It’s really amazing how paper can react when crushed to that point – it appears to very suddenly become incompressible; or at least much, much harder than steel.

      You can get some very, very impressive damage done from thin and harmless looking paper.

      We had a heildberg (now Goss, I guess) M600 running at 55,000iph (roughly 600 meters per minute) – folder jammed, wrapping a steel cylinder. It crushed that cylinder and the adjacent one. Thick steel, just squashed by paper.

      The resulting paper was vaguely reminiscent of ceramic; no discernable sheets/layers at all anymore.

    1. 1. Smoothen & finish the result of that
      2. Pour light glue or something on, so it soaks
      3. Compress again and let dry
      4. ?????
      5. Add feet to have a nice paper table with 2048 layers

  7. It doesn’t take a rocket scientist to understand what’s going on here. The press is applying an incredible amount of energy, it gets converted to heat. The moisture in the paper instantly boils off, the rapid expansion has nowhere to go but out the sides. This is the bang. The paper fuses together as the cellulose molecules become entangled due to the sudden vacuum left behind from the moisture escaping, taking some of the heat with it.

    Ok well maybe not a rocket scientists explanation but the average HaD user gets it.

  8. Someone needs to investigate this. Weigh the paper before and after the 7th fold. If the mass decreased, then it was likely the moisture in the paper being evaporated or otherwise forced out. If it’s the same mass, then it was just the mechanical energy stored in the press when the folder edge broke.

    Bonus points if we can get a high speed camera on it. The comments section demands answers!

  9. I haven’t read all of the responses, so maybe someone else has added this hypothesis:
    Right before the bang, the paper has all sorts of potential energy stored up in it as the fibers are acting like stretched springs under the force of the press. This is mostly at the folds, but I would think that there was a fair amount of tension all over the place. When the “spring” finally fails and snaps somewhere in the sheet, the shockwave that results pushes the rest of the tensioned paper over the edge and causes the paper to disintegrate. We hear some of the released energy as sound, but a lot of it would end up as heat, and this would heat up any resins in the paper, causing the now separated fibers to be glued back together, but now as more of a solid brick. Similar to the process of making sawdust fire logs (heat from pressing the sawdust causes the natural resins in the sawdust to bond the whole thing together into one log).

  10. Hi folks. Before my comment, I must advice:

    I’M NOT STARTING A FLAME WAR!

    Do you have tips of sites that is like the “old HackADay”?

    Please, don’t start fighting with me, with Hack a Day or with each others.

    My question is:

    “I like RED and here is becominig BLUE. You guys are especialist in colors. Where I can find RED again?”

    repeting the advice:
    I’M NOT STARTING A FLAME WAR!

    1. DangerousPrototypes updates fairly infrequently, but they have a lot of that sort of thing. And it seems like there are a lot of oldskool hacks on hackaday.io, but I haven’t been there very often.

  11. Looking at the moment of collapse, it appears to me that two things happen: the paper takes a visible period of time (perhaps 1/10th of a second) to go from its folded size to the compressed size; and the table may be vibrating, rather than springing back to a fixed position. You can see it smooshing out under the weight of the press, so it’s not an instantaneous process, which is interesting but probably doesn’t help explain the process. More interesting to me is the idea that the table may be flexing multiple times, suggesting that there may be multiple waves of tension releasing in the paper as it compresses.

  12. There is quite a bit of trapped air due to the geometry of the paper folded 7 times. Some of those air pockets, under that much pressure, might have undergone combustion (with the volatiles from paper, leftover grease, etc.) and partially oxidized the paper, causing the pockets to collapse (consumption of oxygen) and possibly even crosslink the sheets somewhat. This happens at similar pressures to injection molding (well, at least w.r.t the press – no idea how much the paper sees, because that’s dependent on leakage rate from the air pockets, how sealed they are, etc.) There, if you get a trapped air pocket in your mold due to insufficient venting geometry, you get a bang and burn mark as you form a miniature combustion chamber in that pocket from the air + volatiles from molten plastic.

    Hm, actually seems less reasonable after writing this out. Not entirely sure if there’s enough combustible volatiles at this temperature to actually permit spontaneous combustion at these ratios (but someone should work out the orders of magnitude). I’m still inclined to say some sort of thermal process happened which caused this crosslinking, but it’s hard to really say how this could have been done so homogenously throughout the material, but maybe the numbers work out.

  13. Curiosity killed the cat, as they say.

    I just went out in the shop and tried the same thing. Took a sheet of letter sized paper (8.5×11 inches) and folded it 5 times. Squashed that in the manual hydraulic press with about 20 tons. Folded it once more and squashed that with 40 tons. The resulting chunk of paper showed the same brittle characteristic as seen in his video. It kinda splits apart a bit like slate. There was NO bang, and I could feel no temperature change with my fingers. At the edge of the block of paper, I could still unfold shards and see what was originally laser printed on the sheet.

    I presume the bang in the video is due to his paper suddenly collapsing, allowing the press bed to recoil.

      1. As requested, more results. (Wait for it….)

        First test: 4 sheets of paper, repeatedly cut in half until there was a stack about 0.56 inches tall of 128 pieces, 1.4 x 2.125 inches. Apply forty tons. Uneventful. Note that the diameter of the ram is about the same size as the paper, so force was applied over almost the entire face of the stack. The stack compressed to about 9/32 inch thick, and re-expanded to perhaps 5/16″ thick when force was removed. The resulting stack of paper has turned into a block, although it can be split and individual pages peeled off. The paper has gone from about 0.0045″ thick to about 0.00375″ thick. Once again, no feeling of warmth. Since the pages have become locked together, folding is difficult, with cracking sounds as the pages delaminate.

        Second test: MORE PRESSURE!
        Our press can only do ~40 tons, so the sample must be smaller.
        This time, a single sheet was used, resulting in a sample about 0.7×1.06 inches, same thickness. Back into the press for more squashing. And what do you know? A large bang around 25-30 tons with small bits of shrapnel flying around! The stack has again become a brittle block, about 0.16 inches thick. I attribute the bang to recoil of the press itself, as other parts on the press where shaking and wobbling immediately after. I would say the paper suffered a brittle fracture under compression. Note also the the paper block did in fact feel warm to the touch after the bang. Individual sheets cannot be extracted for measuring.

        Conclusion: squashing paper together forms a bond of some sort. The bond becomes more permanent as the pressure increases. The paper structure becomes brittle as it is subjected to pressure and will shatter like any other brittle material under compressive loads.

        (Keep in mind the above was performed without the use of an Arduino and is not a hack, so shouldn’t even have been reported here.)

  14. Well…

    Whatever you do, if you get the unfortunate job of doing and ‘folding’ laundry, just remember, you can get your stuff out the dryer and just toss you clothes willy nilly into drawers, but if you don’t properly fold your ladies undergarments, she will explode with a force 10 million times of that shown in the video…hence…

    Don’t get your panties in a bunch…just sayin’

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