Costco rakes in billions of dollars every year. It’s not surprising that they make so much money considering they are the perfect one-stop-shop for groceries, gas, home goods, and electronics. But there’s one product that outsells all the rest—and no, it’s not their $4.99 rotisserie chicken. Read up on these secrets behind the famous Costco staple.

It’s actually something that you constantly need to buy but probably hate spending money on. That’s right, Costco’s best-selling item is toilet paper. They sell more than a billion rolls every year. The high quality and warehouse price of Costco’s Kirkland brand toilet paper make it fly off the shelves every day.

Costco actually employs toilet paper engineers to review and test the product before it gets to customers. It might seem like an unnecessary step, but it’s worth it considering they make around $400 million from the product every year. They even use a special tool to test its level of whiteness! These are other Kirkland items you should always buy at Costco.

During the beginning of the coronavirus pandemic in the United States, their toilet paper was flying off the shelves much quicker than it typically does (as it was from every other store that sold toilet paper as well). They were selling out so quickly that Costco had to limit the number of packages customers could buy and stopped accepting returns on toilet paper to prevent people from panic buying more than they actually need. The beloved Kirkland brand toilet paper is slowly starting to reappear on shelves again, but there are some other things that you won’t see in Costco anymore.

You’ll probably think about toilet paper a little differently the next time you use the bathroom.  Next, read up on the secrets Costco employees won’t tell you.