Car Air Freshener Boxes.

Because fragrance passes straight through plain paperboard, and the boxes contaminate each other in storage.

An air freshener works by releasing volatile aromatic compounds into the air. Those compounds are small and they migrate readily through uncoated carton board. Store vanilla next to pine on the same shelf for a few weeks and both boxes — and both products — end up carrying a blend of the two.

Three things follow, and all three cost you:

• The product weakens. Months on a shelf means months of releasing scent into a warehouse rather than into a customer's car.
• Variants blur. A multi-scent range stops reading as distinct products.
• Neighbouring stock is affected. Air fresheners will perfume an entire aisle.

The fix is a barrier lining — a foil or metallised layer inside the carton. It is exactly the same principle as coffee packaging, just working to keep the aroma in rather than oxygen out. It is not a standard carton specification, so it has to be asked for.