Pharmaceutical packaging is obliged to comply with many functions. And it has a huge influence on the quality, effectiveness and applicability of pharmaceuticals. This particularly applies for primary packaging, i.e. packaging which comes or can potentially come into direct contact with the dosage form, such as ampoules, ready-to-fill syringes, blister packs, pharmaceutical stoppers or other types of pharmaceutical seals. Therefore, the requirement profile – protection, safety, compatibility and function – needs to be complied with as early as the packaging development phase. Furthermore, test certificates in accordance with USP 381 are required for pharmaceutical stoppers (and other pharmaceutical seals) as primary packaging. What is behind all this? As a general rule, the USP 381 regulates the properties of pharmaceutical seals (elastomeric closures for injections). Specifically, it includes both the certificate of bio-compatibility and physical-chemical tests and functional tests.