Pack-off rubbers, also called blowout preventer elements, provide emergency sealing by compressing around the wireline. Hydraulically or manually actuated, they close off the wellbore if grease seal fails. Tough HNBR or Viton compounds resist tearing and extrusion under rapid closure in critical safety scenarios https://globalsealstech.com/product-category/oil-gas-seals/oil-free-lubricated-pump-seals/