Bill Sampson

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.

What's a disordered material?

And there are sort of clearer patches.

When we saw the fibre pulp being bashed about in the paper mill, it was actually very controlled damage.

How much the fibres are refined at that stage determines the type of paper you end up with.

Basically, more refining lets the fibres pack together more tightly, meaning more bonds between the fibres and a denser sheet.

While less refining means the fibres form fewer bonds and end up with more space around them.

What kind of scale are we talking about here?

Because I'm kind of picturing long fibers stretched over the fold, but are they smaller than that?

So we've got lots of different kinds of paper in front of us on the table.

We've got some origami paper.

We've got tracing paper.

And when I fold tracing paper, I mean, it really is unforgiving, isn't it?

That fold is basically stuck there.

Yes, it has.

The fibres in tracing paper are about as densely packed and strongly bonded as you can get.