Mystery solved

I’ve always wondered why bags of chips (crisps) are only one third full.

I’ve always just explained it away as marketing greed; manufacturers making their bags look bigger than the contents.

But, no, there is a purpose to all that free volume.

In an aeroplane at altitude these bags puff up to the max but don’t pop.

It must be a finely judged thing. Respect to the genius who figured this spec out.