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CrowdScience

Why does paper fold so well?

12 Jun 2026

Transcription

Transcript generated automatically by AI and may contain errors.

Chapter 1: What inspired Haruka to ask about paper folding?

0.031 - 3.696 Caroline Steel

This BBC podcast is supported by ads outside the UK.

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6.123 - 52.532

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54.52 - 62.453

We'll start by creating the structural creases. So place your paper with the colour side down. Colour side down, OK.

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62.934 - 85.389 Bill Sampson

You're listening to Crowd Science from the BBC World Service, the show inspired by your curiosity. Fold the paper diagonally. And sometimes by your skills. corner to corner, ensuring the edges align precisely. Crowd science listener Haruka is helping me make an origami crane over a video call from Tokyo, Japan.

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85.93 - 92.998

A paper crane is a symbol of longevity and healthy life, so it's special and iconic to us.

93.839 - 107.621 Bill Sampson

Origami is a Japanese word that literally translates to paper folding. So the paper should naturally follow the creases you made. And this is my first attempt at it. I'm struggling.

108.462 - 117.318

Why do you want to go the other way? Go this way. The bottom side of the kite should be lifted to the top.

117.659 - 135.723 Bill Sampson

I have bad news. My kite doesn't have any flaps. So I think I managed to do the whole thing the wrong way around then. Yeah. Okay, so I'm going to keep working on my crane. In the meantime, I should ask you about your question.

136.644 - 144.937

My question for crowd science is, why is paper folding irreversible? Or why does paper fold so well?

Chapter 2: How is paper made and what affects its foldability?

242.221 - 259.639 Bill Sampson

But why does paper remember its creases in a way that, say, a cotton napkin doesn't? First, I think we need to find out exactly what paper is. I know it usually comes from trees, but how can a knobbly old pine make a crisp white sheet?

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261.762 - 266.911 Dr. Steven Mann

So we make the stuff in the beater and then we pump it into here, into this chest.

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267.572 - 285.424 Bill Sampson

To me, it sort of looks like fermented milk, kind of like cottage cheese. It's like white and lumpy. We're being shown around this very noisy paper-making operation by Dr Stephen Mann. He's a paper chemist, paper-making teacher and a trustee here at Frogmore Paper Mill.

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285.556 - 292.563 Dr. Steven Mann

And this is the place where the world's first paper machine was commercially run and built around 1803.

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293.043 - 300.231 Bill Sampson

And so this is a historic paper mill. How different is it from a modern one? Is the process of making paper the same?

300.771 - 305.676 Dr. Steven Mann

The process is the same. Paper was invented by Ceylon 105AD.

306.257 - 311.682 Bill Sampson

Ceylon was a Chinese court official credited with inventing paper about 2,000 years ago.

311.712 - 318.894 Dr. Steven Mann

He's known as the father of papermaking purely because he was the guy who actually wrote down the methodology for making paper.

319.376 - 323.95 Bill Sampson

So could you talk me through the process of how paper is made?

Chapter 3: What types of paper are best for origami and why?

537.508 - 547.361 Dr. Steven Mann

Yes. And the hydrogen on that will be attracted to the oxygen. And that's a phenomenon that we call hydrogen bonding. And without hydrogen bonding, we'd all be lumps of jelly on the floor.

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548.302 - 550.745 Bill Sampson

And paper would be lumps of jelly on the floor as well.

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551.006 - 552.207 Dr. Steven Mann

You wouldn't have a sheet of paper.

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552.407 - 559.255 Bill Sampson

So this bonding between an OH on one fibre and an OH on another fibre is crucial. They're kind of sticking together.

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559.516 - 573.312 Dr. Steven Mann

Nature makes the OH groups when it makes the glucose molecules. And the paper maker gets the OH groups on one fibre as close as he can to the OH groups on another fibre so that the bonding can happen.

573.68 - 586.322 Bill Sampson

The paper-making process of refining the fibres then squashing them together allows lots of sticky hydrogen bonds to form. And those hydrogen bonds are partly why paper folds so perfectly.

586.471 - 608.637 Dr. Steven Mann

If you think about the sheets of paper, you've got the fibres themselves and you've got the fibre-fibre bonding. If you put a crease in the paper, what you're actually doing is you are destroying some of those hydrogen bonds and they've gone forever and you can never undo that damage. And the other thing you do is you damage the fibres.

609.418 - 621.12 Dr. Steven Mann

Some fibres you will break, some fibres you will partly break, and some fibres you won't break. So for that reason, once you've creased a piece of paper, you can't really uncrease it.

621.361 - 626.831 Bill Sampson

So the only way to get rid of the crease would be to sort of pull it all apart into fibres again and put it back through the mill.

Chapter 4: How does the structure of paper contribute to its folding capabilities?

787.195 - 811.622 Toshiko Kurata

It's usually handmade. Got some gorgeous patterns. Yes, very beautiful design. And this is made from the mulberry. Also maybe koso, so different type of the tree. Okay. You can see the... I can see the plant fibres, yeah. Yeah, so like made from long, natural plant fibre. Feel like cloth-like. Yes, it feels a bit cloth-like.

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811.642 - 818.893 Bill Sampson

Yeah, and it's softer. So we've got Washi in front of us, we've got Kami in front of us. What would be best for making a paper crane?

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818.873 - 822.296 Toshiko Kurata

So, all kind of paper are able to make.

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823.077 - 827.52 Bill Sampson

Here we go again. Time to make the most of paper's handy hydrogen bonds.

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827.78 - 832.885 Toshiko Kurata

Please face up to the colour side and try to make the triangle, please.

833.305 - 841.372 Bill Sampson

We're making movable cranes, and for this, Toshiko chooses the washi paper and recommends that as a beginner, I use cami paper.

842.973 - 845.535 Toshiko Kurata

And always better to make a very sharp crease.

846.196 - 847.617 Bill Sampson

OK, really press down on it.

847.637 - 847.897 Toshiko Kurata

Yes.

Chapter 5: Why is paper folding considered irreversible?

943.8 - 945.122 Bill Sampson

Can I try flap your crane?

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945.262 - 946.163 Toshiko Kurata

You will see.

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946.183 - 954.375 Bill Sampson

Ah, yeah, it's much smoother. It's also, it's less resistant. Like I have to apply less force to make it flap.

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954.655 - 958.62 Toshiko Kurata

Yeah, this one I kind of feel fleary to fly away.

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958.681 - 989.62 Bill Sampson

My crane looks pretty good, even if I do say so myself. Its flapping motion is a bit stiff, but I love it all the same. So why is washy paper perfect for a smooth flap? Why is cami paper ideal for beginners? And why is tracing paper, paper you can see through, so unforgiving? We're heading to Manchester in the UK to meet a professor of paper physics who I'm hoping can solve our paper puzzles.

990.381 - 997.988 Caroline Steel

My name is Bill Sampson. I'm a professor in the Department of Materials at the University of Manchester and I study disordered materials, one of which is paper.

998.525 - 1000.047 Bill Sampson

What's a disordered material?

1000.748 - 1010.218 Caroline Steel

OK, something like paper is very much formed by random processes. The fibres are very, very much disordered in the plane. And if you hold a piece of paper up to the light, you can see it's sort of cloudy.

1010.739 - 1013.021 Bill Sampson

And there are sort of clearer patches.

Chapter 6: What are the differences between various paper types for folding?

1179.239 - 1189.117 Caroline Steel

They're about 20, 30 microns wide. And you can see that where I ripped the sheet, it's gone through layers, and that's because paper has a layered structure. This origami paper, I did a few calculations, is about eight fibres thick.

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1189.738 - 1198.834 Caroline Steel

And that layered structure is one of the reasons why it folds so nicely, is because the fibres are lying on top of each other, and therefore they can bend over each other and buckle into the spaces, into those voids between the fibres.

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1199.101 - 1201.692 Bill Sampson

Could we have a go at folding it and seeing what a fold looks like?

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1201.732 - 1208.942 Caroline Steel

What I'm going to do is I'm going to fold it and then I'm going to score it with my fingernail. Now, if I get that under the microscope, you can see the line.

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1208.973 - 1212.278 Bill Sampson

very clear fold under the microscope. There's sort of a dark line.

1212.598 - 1232.787 Caroline Steel

And if you look along there, I did manage to find some fibres that were just starting to come out of the surface along the crease. You can just see there's some that's just starting to poke out a little bit. Now, I did some calculations about this kind of paper last night, and one centimetre of this paper would have about 3,000 fibres crossing it. So we're just breaking the odd one here or there.

1232.767 - 1235.711 Bill Sampson

So it's unsurprising that the odd one is breaking.

1235.731 - 1240.316 Caroline Steel

Right, exactly. But it's an example of this. You've got this kind of damage that's happening in there, but it's very, very few.

1240.937 - 1265.252 Bill Sampson

It's time to bring out the cranes Toshiko and I made earlier. Why do they behave so differently from each other? We've made some paper cranes, one out of cami paper. They flap. And one out of washi paper. They flap. And I think you can kind of hear that the washy one flaps more smoothly. Why is it smoother to flap?

Chapter 7: How does technology enhance origami design and complexity?

1384.738 - 1390.064 Bill Sampson

I mean, it's so impressive. And on the surface, there are these little triangles.

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1390.785 - 1416.212 Tomohiro Tachi

Yeah, so this three-dimensional form is made of small triangles. So that's how you model 3D models in computer graphics. And the algorithm is computing some origami folding between these triangles to make it foldable from one sheet of paper to that given shape. For that, I used some compression geometry techniques to design this.

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1416.773 - 1428.992 Tomohiro Tachi

I designed the software to do so because I thought I cannot make it by myself to arrange all of these triangles. You have to compute all of the creases all at once.

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1429.192 - 1440.269 Bill Sampson

OK, clever. So you can put the information into your software about what you want to make and the software can kind of spit out a solution in a way. This is how you could do that.

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1440.289 - 1441.01 Tomohiro Tachi

Yes, that's right.

1441.23 - 1443.393 Bill Sampson

So does a machine do the folding for you?

1443.794 - 1449.883 Tomohiro Tachi

So the computer tells you the crease pattern where you fold, but you have to fold by your hands.

1449.998 - 1451.52 Bill Sampson

Amazing. How long did it take you?

1452.201 - 1457.068 Tomohiro Tachi

So this took me 10 hours or so to fold from one piece of paper.

Chapter 8: What are the broader applications of origami principles beyond art?

1663.935 - 1673.771

If you have a question you'd like the team to unfold, please email crowdscience at bbc.co.uk. Thanks for listening. Mata ne.

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1674.732 - 1686.792 Bill Sampson

Thanks, Haruka. And don't forget, you can also send your questions to us on WhatsApp. Just message us or send a voice note to plus44 8000 314 773. Bye.

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