From Guild Wars 2 Wiki
Double-click to consume.
Double-click to increase the maximum stack size of all stored materials by 250.
— In-game description
- A maximum of 7 Storage Expanders may be purchased per account, for a maximum stack size of 2,000.
- This only applies to the material storage tab in the bank. Moving a stack with more than 250 items in the material storage tab out of the material storage tab will result in either several smaller stacks or only 250 items withdrawn.
- The upgrade limit was increased by 2 on the 12th of February, 2016. Prior to this, the maximum stack size was 1,500..