A coaster, drink coaster, beverage coaster, or beermat is an item used to rest drinks upon. Coasters protect the surface of a table or any other surface where the user might place a drink. Coasters placed on top of a beverage can also be used to show that a drink is not finished or to prevent contamination (usually from insects). Coasters can also stop hot drinks burning the table surface.
This How To Make Coasters app contains illustrated instructions for: