Everyone in the humid eastern US needs these coasters. They are the answer to sweating glasses. We have been using these for over 20 years on our wooden tables. I bought these because I just wanted a change, sick of looking at the old ones! Don't buy the cheap knock-offs from Wal-Mart and Target. If they have a picture or design that is shiny on them, they do not work. The extra bucks for the good ones are worth it. Much cheaper than oak or walnut tables.