A filter's micron rating is the size of particle it captures, measured in millionths of a metre. A 20-micron filter traps anything larger than 20 micrometres — skin cells, hair, grit — while letting water through freely. Lower numbers filter more finely but restrict flow and clog faster.
Why it matters when you are comparing products
Micron rating tells you what the filter removes, and nothing about biological contamination. Filtration and sanitation are separate jobs that both need doing.
Where this comes up
- How do you keep cold-plunge water clean? — Where filtration fits in the maintenance routine.
Reviewed 2026-08-15