Crimp closure, N 20, alu., center hole, Butyl dark gray/PTFE gray, 3.0 mm 70234

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.