How can I display a Material Metafield on an invoice?

I have made a Material Metafield for all our product (product.metafields.my_fields.material).
I want to include this on our invoice & packing slip for each product.

How can I call this metafield out and include it in the invoice?

Perhaps, the best way to do that is to retrieve the data from the line_item object once an order is created. Here’s the link to a similar thread.