This is a low investment (only about 60g each side) master spool scaled for polymaker refill spools. For me these came out as press-fit into the cardboard.

I thought this design was pretty so I used it as a base despite the fact that the sticker from polymaker has no spot on it. If someone wants to remix this with a view window and a space for the sticker that'd be great!

No support needed, just print 2 of these and press them into each side of the refill spool.

I used PETG in case I need to dry out any of the spools later. PLA can sag if put in a heat-based filament dryer.

EDIT: As I've made a few of these, 2 out of the 10 spools I've used were too loose for a press fit. I put some blue tape on the inside of the cardboard as filler and that worked great.