What are fungible materials?

Fungible materials are identical materials you can't tell apart once they're mixed, like steel coil from two mills or grain in one silo. When some originate and some don't, you can split them by an inventory method instead of keeping them physically apart.

How it works

Most agreements accept recognised inventory methods, such as first in first out or averaging, as long as you use one consistently. The EU and the UK call this accounting segregation, and under some of their agreements you need customs' permission before you use it.