Polystyrene beads are tiny beads of the polymer polystyrene. Polystyrene is a petroleum-based product with thermoplastic properties. In its original form, polystyrene is a hard plastic, but it can be expanded to make a styrofoam-like product. Polystyrene is often used in beanbags because it is inexpensive, comfortable, and long-lasting. You can order it online from discount stores such as Kmart.
You can also use packing peanuts to fill beanbags. Packing peanuts are now made from a variety of materials, but the most common material is polyethylene, which is a petroleum-based product similar to polystyrene. Packing peanuts are larger than polystyrene beads, so they'll have a different feel in a beanbag, but they're lightweight and usually recycled. You can buy them at postal stores such as Mailboxes, Etc. Make sure you don't get the kind that dissolve in water.
Traditionally, beanbags were filled with beans. These days, people want something a little more comfortable to sit on. However, combining dried beans with another filler such as packing peanuts or polyester stuffing makes a great beanbag. The beans give the beanbag some heft and structure, and the stuffing helps to soften the beans.
Cedar shavings smell good and repel fleas. For this reason, cedar shavings are often used for beanbags used by pets. However, you could also experiment with using cedar shavings in beanbags used by people. As with the dried beans, combine the shavings with a softer medium for maximum comfort.
If you have an old down comforter or down pillows that you no longer use, recycle the feathers by putting them in a beanbag. Feathers tend to lump together, so you might want to try combining them with cedar shavings, beans or polystyrene beads for the best effect.