The UK's Snack, Nut and Crisp Manufacturers Association recently told the Daily Mail, the "empty" part of the chips keeps the products from going stale and prevents damage to the chips.

This is called 'functional slack-fill' which is unavoidable and is needed to prevent the precious chips from getting crushed.

And the "air" inside is actually nitrogen.

The Snack, Nut and Crisp Manufacturers Association spokesperson, added, "in addition to preventing staleness, the inserted gas also provides the added benefit of creating a cushioning effect to protect the fragile contents of a packet from damage."

"The packaging expands or contracts depending on the ambient temperature, whereby the gas presents in the pack will fill a larger volume when it's hotter, and a smaller volume when it's coolers."

"For this reason, the packaging is required to be of a certain size to accommodate the potential expansion of the gas."

But do companies actually put the right amount of product in these "empty" bags?

Robert Niemman, a San Francisco-based lawyer specialising in food-related lawsuits, told Vox, "Slack fill occurs [most often] in snacks, nuts, candy. The weight is always accurate. If it says there's two pounds in there, there's two pounds, probably a little bit more."

"But if the container is designed to hold four pounds in there, obviously it's only 50 per cent full. The container is larger than necessary for the amount of product that's in there, so it gives a deception of how much there is. It's always accurate by weight."