Coasters

https://www.oed.com/dictionary/coaster_n?tab=meaning_and_use

https://britishbeermats.org/beermats/beermat-history/

https://scholar.uwindsor.ca/cgi/viewcontent.cgi?article=1020&context=llcpub

Kenneth Osborne and Brian Pipe, The International Book of Beer Labels, Mats, and Coasters (London 1979)

https://stompstickers.com/blogs/articles/history-of-the-drink-coaster-who-designed-it-why

https://www.thebeerprofessor.com/?p=991