Proof coin sets are produced by the US Mint using a process that brings out the beauty of each coin's design.  The dies and planchets (the metal disks that will become coins) are polished before the coin is struck.  This gives the fields (blank areas) a mirrored look and the image a frosted effect.  Proof coins are struck twice, giving each coin a sharper design and rims.  The proof sets are packaged at the US Mint and display America's coins at their best.