These closures with molded Butyl/PTFE septa are only laminated with PTFE in the contact area with the sample. Thus the elastomeric Butyl can achieve on the vial's glass rims a very tight seal, while in comparison a completely PTFE covered septum would have a very slippery surface on the glass and could easily be twisted around. These typically called "Pharma-Fix" closures have a good analytical purity. The bridges of the cap's scorelines break open at an internal vial pressure exceeding 3 bars (± 0.5 bars), thus releasing overpressure in a crontrolled way. Functionality of the cap is not depending on the design of the vial's crimp neck (beveled top, flat crimp neck).