Bean bag chairs are fabric sacks filled with polystyrene beads. They vary in size, cover fabric and quality.
I thought bean bags were filled with polystyrene packing pellets. I made a tube-like sack out of an old sheet, and another one, same size, pieced out of thick, colorful upholstery samples. I filled the plain sack with packing pellets remaining from several shipments. Turned out I didn't have infinite supply of this garbage -- the average size bean bag chair takes ten to twelve cubic feet of filling. I had to collect more from a small local store which sold hand made vases and lamp shades. The store had several shipments a week and was rather happy to share. I pulled the pieced bag over the filled plain one and tied the ends. My chair survived five years of abuse by toddlers. I washed the cover several times and refilled it once. Recently I decided it was not worth fixing fraying seams of the pieced cover and disposed of it.
Actually, bean bag chairs sold in stores are not filled with packaging pellets. They are filled with firmer polystyrene foam that can be virgin (new, pre-consumer), or recycled (post-consumer). Recycled polystyrene beads come from used (typically once) molded packaging, crushed to 1/4" size pieces. Virgin beads come this size right away. People who sell bean bag furniture with new filing claim it's more resilient, while people who recycle claim there is no difference and point at conservation virtues. There is no reason to expect different performance. Nobody bothered to really test new vs. used filling. Practically, Styrofoam beads compress and cramble with use and have to be replaced once in a while. How often, depends on your expectation of comfort and manner of use. As I mentioned, I replaced my lower quality filling after two years of pillow fights. Polystyrene is cheap. It doesn't decompose and it doesn't recycle beyond reuse as filling.
Besides the origin of filling, bean bag chairs differ in size, color and quality. Typical sizes are kid's (110" round flat), large (130" flat) and oversized (180" round flat). Target have small non-washable bean bags as cheap as $19. Large bean bag loveseat with removable fake fur cover can cost as much as $350, more than a low-end IKEA sofa, but arguably more comfortable. Typical price for a typical dorm chair is $50-$100. Most of bean bag chairs are round, some are pear-shaped. They come in bright solid covers, denim, vinyl and fake fur covers, and theme covers: dinosaurs for kids or university logos for college kids. I never saw pieced covers except the chair I made myself.