The Katadyn Hiker Pro Replacement Cartridge replaces old, scummy cartridges from your Katadyn Hiker or Hiker Pro microfilter. The Hiker Pro Cartridge uses the same awesome microfilter element, but wraps it in a protective membrance that makes it a snap to service in the field. Clogs will be less common and easier to fix if they do. When you're out in the wilderness, you just need the water, not the nasty things living in it.