Do you have issues with filament samples, which are without spool? Or don't you know what to do with last 20m of filament on the spool? 

I designed spool splitter specially for Prusament spools. 

Instructions:

1. Print spool splitter (you can choose one of the sizes 
   1. 200 mm - original Prusament spool diameter
   2. 180 mm - diameter for printing on Prusa Mini
   3. 150 mm - smaller diameter (in my opinion best size for last 20 m of filament)
   4. 135 mm - cute, small diameter suited for 10 m samples
2. Remeasure your paper central tube and eventually resize inner diameter. My paper tubes are usually D99.5 mm. I recommend add 0,1 mm in inner diameter
3. Print your spool splitter
4. Disassemble original Prusament spool
5. insert spool splitter (you can add many splitter as you want)
6. Insert filament in small hole close to paper tube
7. Close the spool
8. Wind your filament!

Enjoy your printing and storage!