They = quite a few brands so far. The ones I know of include microcenter (inland), fiberlogy, sunlu, and esun. I’m not sure how many are interchangeable but they sell the refills wound onto a cardboard tube/core with a few straps keeping the winds from falling to the side since there are no spool sides to keep it in place. You slot the cardboard core onto your reusable spool sides and once attached you can cut the straps to release the filament.