Kent Micronite filters contained blue crocidolite asbestos. Of the 6 known types of asbestos, crocudolite is the most toxic/harmful.
One study revealed smoking a pack of Kent Micronite cigarettes every day for a year would expose a smoker to 131 million carcinogenic crocidolite fibers.
A 1989 study of 33 people who worked in the Hollingsworth & Vose filter factory in 1953 found 28 of them died from asbestos-related diseases, including asbestosis, lung cancer and mesothelioma.
(actually speakeasies referred to illegal bars during prohibition from 1920-33, while the cigarettes came out in 1952 🤓 (unless it continued to be used as a slang term in the 50s))
They continued to operate as bars once bars were legal but often had major renovations since they no longer had to be hidden. A few friends of mine lived in one. Only house I've ever been in that had a larger basement than the house.