Money, also known as Cash, is the main currency in the Bloons Tower Defense series. You use money to buy towers, upgrades, and other special items. In Bloons TD 4 and Bloons TD 5, the player can buy a Premium Upgrade called Double Cash Mode, which gives the player twice the money for each bloon popped and also starts the player out with twice the regular amount. You can't get money in Deflation Mode. Money has a "maximum limit", that amount depending on the type of game it is played on. Bloons TD4 iOS is at about $81,000,000, at that point the money increasing slows down to a crawl of normal. Bloons TD 5 Deluxe is at precisely $45,000,000, you can't go any higher even with abilities or anything. The rest have no known cap.