https://www.iso.org/standard/57902.html
"Bio" BBs are made out of PLA:
https://en.wikipedia.org/wiki/Polylactic_acid
And typically made out of corn or manioc starch, or even cane sugar.
Precise weight is controlled via barium sulfate.
There's a small coating of varnish to make it smooth as well as a bit more resistant to external conditions, otherwise they would degrade too quickly.
https://www.iso.org/standard/57902.html
"Bio" BBs are made out of PLA:
https://en.wikipedia.org/wiki/Polylactic_acid
And typically made out of corn or manioc starch, or even cane sugar.
Precise weight is controlled via barium sulfate.
There's a small coating of varnish to make it smooth as well as a bit more resistant to external conditions, otherwise they would degrade too quickly.