Are cork coasters waterproof?

Cork Coasters are water-resistant but not entirely waterproof. 

While cork has natural water-resistant properties, they can become damaged if constantly exposed to water without drying. We recommend allowing them to dry after exposure to water.

One final consideration is that people drinking at a bar, may subconciously pick at the coaster as their night progresses. When soaked with water, the coaster may be easier to break apart.