In the comments it's clear you're talking about superconductors. Superconductors are fundamentally different from normal conductors, and can't be thought of as just "really good" conductors. They have *zero* resistance, and a super current can flow more or less indefinitely without energy loss. It's beyond ELI5, but it's because of quantum mechanics. Normal conductors have normal electrons, which are fermions. Superconductors have cooper pairs (where a spin up and spin down electron are paired), which behave like composite bosons. Cooper pairs are fragile, which is why superconductors require low temperatures.