A celtic themed coaster I made as a gift this year, inspired by several other coaster designs I found. They are 90mm in diameter and there is a fitting holder included here. Both are optimized for printing in two colors and with a 0.6mm nozzle, so that wood-filled filaments can be used.

For a nicer look and usability, I attached adhesive felt pads of roughly 1.3mm thickness to the bottom of the coasters, resulting in a total thickness of 4.3mm per piece. With that, the holder can hold 5 coasters, without felt pads it can hold 8.

I recommend printing the top layer or the complete emblem with as many perimeters as possible. This prevents tiny infill moves, which look/feel rough with most printers (mine included). I've uploaded a screenshot to illustrate this. If your slicer supports it, It's also a nice feature to use "Hilbert Curve" as the top infill method, because it gives a somewhat natural texture.

If you print them please post a make and tell me in the comments if yours happened to have any problems with hot drinks.