The cap is made of aluminum. Aluminum is commonly used due to its excellent sealing properties and resistance to corrosion. The septa is a critical component of the cap and is made of silicone or PTFE (polytetrafluoroethylene). It is positioned inside the cap and serves as a barrier between the sample and the external environment. The cap has a crimp top design, which means it can be securely attached to the vial by using a crimping tool. This process involves crimping the cap around the vial’s neck, creating a tight and tamper-evident seal. These caps with septa provide an effective barrier against contamination, evaporation, and changes in sample composition, ensuring that the sample remains stable and reliable for analysis.