[Peterz_shu]

It has a lot of air gaps within its fibers.

We know that Solids CANNOT be compressed. So what's actually being folded is the air gaps.

Which is why you can't easily fold a piece of tungsten. It has less air gaps.

[gruez]

But you can fold aluminum foil just fine? That certainly doesn't have "a lot of air gaps within its fiber"

[dotancohen]

Actually I've never had success cleanly folding aluminium foil. There are always imperfections and creases.

[IAmBroom]

Pretty sure the material's innate stiffness plays a role there, too.

Metallic film folds quite nicely.