Medical Halogenated butyl tetra fluoroethylene film (ETFE)series
https://www.klstopper.com/product/coated-rubber-stopper/halogenated-butyl-tetra-fluoroethylene-film-etfe-series.html
By adding a ETF or TEFLON on the surface of the rubber stopper, could prevent the contact from stopper and the drug, which can effectively reduce the absorption, and infiltration between the rubber stopper and the drug.