These are 3D printed coasters with slots for tiles. I thought it was a more interesting look than using 100% plastic. I used bathroom mosaic tiles from Lowes. The tile slots are 23.5mm x 23.5mm x 10mm. The tiles fit pretty snugly but I secured each one with a dot of hot glue to make sure they stay put.
I printed mine in PLA at 195 with a 50 degree bed. The first one I printed unheated and it warped pretty badly so for the second one I used heat and glue.