Dry Erase Dungeon Tiles: Wire Mesh Square Booster Pack - Rules of Play says:
Role 4 Initiative has now expanded its lineup of Dry-Erase Dungeon Tiles to include booster packs! These smaller sets of two 10" tiles and eight 5" tiles give the gamer a cost-effective way of expanding their R4I Dungeon Tile roster to include different colors or genre. Compatible with dry-erase, wet-erase, and liquid chalk markers, these double-sided tiles offer much more flexibility and expandibility than traditional vinyl mats.