The SP's are pigment based pens that are alumninum bodied, refillable and have replacement tips. They are waterproof, acid-free, archival, and photocopy safe; they won't dissolve toner.
One size cartridge works for Color SP pens with both 0.3mm and Brush Multiliner SPs.
Multiliner SP inking pens are pigment based, and provide the highest quality for all your inking needs. Ink cartridges and replacement nibs are available so you never need to throw these durable aluminum bodied pens away.