Quick Answer
Redox (oxidation-reduction) is an electron-transfer reaction. In shower filtration, copper-zinc media like KDF-55 use redox to alter certain substances — notably free chlorine — and the reaction performs well at warm shower temperatures.
Problem
'Redox' is technical jargon on filter packaging. Understanding it helps explain why some media work better in hot shower water than others.
Product Recommendation
ZOOSHEN High-Output and Multi-Stage systems combine KDF (redox) with activated carbon. See /technical/kdf-55 and /compare/kdf-vs-carbon.