The same thick grey chipboard as the large 3D shrines. Artist Trading Coins are 2-1/2" diameter.
Hint: as the diameter of a coin matches the width of an ATC, all the collage sheets designed for ATCs can be used as an image on a coin (in addition to collage sheets specifically designed for Art Coins, like the Art Coin Starters Collage Sheet linked below).
One of the extra photos above shows one of these coins inside a 3 Inch Wallet (one of a big bunch of “holders” (pockets/wallets/folders) designed to fit the 2-1/2" diameter Art Coins or Coasters announced with the May 2019 kit).
Set of 3.190428RT 190512KB art coin 190523DC artcoinlink GND gryGD 190428coinkit 190428new 190516NB 190509SK 190530SC