Polymaker is a Chinese supplier, selling to California residents, while also running ad campaigns through ghost gun content creators aimed at California residents, defining themselves explicitly as a ghost gun ingredient.

If they didn't want to get caught up in this, they shouldn't have gotten involved in the illicit arms business. But they wanted to be known as the plastic supplier that is cool with you making ghost guns, and that isn't going to fly in California.

Plastic suppliers that don't advertise themselves explicitly as being part of the ghost gun supply chain will be fine.