These coasters are made of 3 MM Sturdy MDF Boards with glossy finishing. The size is 3.5 inches.
The printing is directly done onto the coaster, unlike other similar products that make use of a sticker on the MDF/wood board. Since we use no sticker, but advance direct printing technology, you get a practically usable, gift-worthy premium product, for a only a slight extra cost.
Summary: Do not compare this with the inferior, slightly cheaper coasters you might find on other sites, which use stickers that come off in a very short time.