Center tear off caps are crimp caps with tamper evidence. In order to be able to access and penetrate the septum, the middle cover needs to be removed from the center hole. This product is a closure with a molded Butyl/PTFE liner that is 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.