Paper towels have been in and out of stock on Amazon (AMZN), Costco (COST) and local stores. And when paper towels are available, customers can’t always get the brand they want.

Part of the reason for the shortage is people keep hoarding them: there was a massive surge in sales of Bounty paper towels in July, Procter & Gamble (PG) reported, as customers swept them off store shelves.

But the shortage could also have something to do with the way companies produce the paper towels. Lean manufacturing, in which companies make only as much product as they believe customers will buy on a given day — has borne the brunt of the blame for the shortage. Last month, the Wall Street Journal published an article called “Why are there still not enough paper towels?” laying blame primarily on paper towel manufacturers building their operations to keep costs to a minimum.