A silver chloride layer thinner than a human hair is all that stands between your heart’s electric field and an amplifier’s input stage. Printed ECG electrodes on flex are electrochemistry disguised as manufacturing. The body carries current by moving ions. Silicon carries it by moving electrons. Something has to translate, and that translator is the electrode. Silver/silver chloride wins because it is non-polarisable. Chloride ions in sweat and interstitial fluid exchange freely with the AgCl layer, so charge crosses the interface as a Faradaic reaction rather than piling up on a capacitive double layer. That gives a stable half-cell potential and minimal baseline wander, which matters when the signal you are chasing is only 0.5 to 5 mV riding beneath mains pickup orders of magnitude larger. The stack is deceptively simple: - Substrate: polyimide, PET or TPU, 25 to 125 µm - Conductor: screen printed silver ink, 8 to 15 µm wet - Sensing layer: Ag/AgCl blend, typically 80:20 by weig...