The Blank Voucher in Balatro initially appears to do nothing when purchased, as its description states "Does Nothing?" However, its true purpose is to serve as a hidden progression mechanic. When you purchase the Blank Voucher a total of 10 times across different runs, it unlocks the Antimatter Voucher. The Antimatter Voucher is a powerful upgrade that grants you an extra Joker slot during your run, allowing you to include one more Joker card in your deck, which can significantly boost your power

. You can buy only one voucher per run, so unlocking the Antimatter Voucher requires multiple runs. There is also a known method to speed up this process by purchasing the Blank Voucher and then quitting to the main menu without leaving the store, repeating this 10 times to trigger the unlock quickly

. In summary:

• The Blank Voucher itself does nothing when bought.
• Buying it 10 times unlocks the Antimatter Voucher.
• The Antimatter Voucher adds +1 Joker slot to your deck.
• This unlock enhances your deck-building options and overall power in the game