Coasters are one of those things you learn to appreciate as an adult. No one wants to ruin good furniture with a water ring. (Although, if you are crafty you can turn those water rings into a new design!)
I hate the feeling of instability when blindly setting a cup down on a ceramic coaster. These silicone coasters help me feel secure when I'm setting my glass down, no matter what else I'm doing. They come in a set of 8, although when you first take them out of the box it only looks like 4 due to the packaging. (You have to pull them apart. And let me tell you, silicone is grippy!) Since they are silicone they have like to stick where you put them. I haven't tried sticking one to the mirror, but I wouldn't be surprised if it stayed there. They are advertised to be non slip and that is definitely true! I set one on a slope and it kept
my drink in place!