Firstly, we recommend using only EPS beans (those little white ones about the size of a small pea) as they allow the bean bag to hold it's shape and provide a comfortable and supportive experience. While memory foam is popular, it only works for those large round floppy bean bags.
You can buy bean bag beans (EPS beans) from most "big box" retailers, in store or online, such as Amazon and Walmart. Simply search "bean bag filler" on any of those online stores. The cheapest beans we've found are 100 Liter bags for about $20 on Amazon and you can buy them with the link HERE.
You'll need 200 Liters of beans for the child size and 300 Liters for the adult size. *Note: if you click on the picture links above to buy on Amazon and you need 300L, don't choose the 300L option from the dropdown as they want to charge you over $100 for 300L. The cheapest option is to choose 200L for $36 and add to cart and then 100L for $19.
Don't forget to check out our bean bag filling instructional video HERE.