system
Given the following post, respond as if you're commenting on Reddit:
human
[Fallout] are bottle caps good currency? if so what are the limitations of them?
gpt
Bottle Caps were originally used by traders at The Hub and backed by water. IIRC, one bottle cap was originally worth a Nuka Cola bottle worth of clean water. 

The technology needed to produce more bottle caps has been (kinda but not really) lost after the war. It's entirely possible to create a new bottle cap by hand but the process is so time consuming it's not worth it.

For a time, bottle caps were phased out and replaced by NCR dollars which were backed by gold. Unfortunately, the NCR gold reserves were destroyed and people reverted back to bottle caps.