Our assessment
This is a manufacturer-document review, not a use test. We checked the 766 one-liter Juice Jar, sold in sets of three by WECK’s US importer.
For drinks kept at home, it answers the closure question simply: the jar and lid are glass, and the seal is a natural rubber ring. It is a storage jar, and WECK says only water-bath canning makes the seal airtight, so it is not a bottle for a bag.
No study we found has measured particle release from these jars or rings. A jug or bottle you already own and like is a fine place to stop.