system
Given the following post, respond as if you're commenting on Reddit:
human
Quick question, how does a rocket engine like Merlin 1D NOT melt the rocket's nozzle?

What kind of material withstands so much heat and energy from that kind of rocket engine? How can they be reusable? I saw a testing video from SpaceX that lasted 3 mins and couldn't stop wondering how is it that the nozzle of the engine didn't melt away.
gpt
Those engines have cooling channels in the nozzle where cold fuel is circulated before it's being injected in the engine. Some of them will also inject a thin layer of cold gases along the inside walls of the nozzle to cool it down.