That was gettin' heavy!
— The Engineer
The Backpack Expander is a tool item that appears as a backpack held together with four straps that has a Description Tag, Heavy Duty Rag, two Mann Co. Supply Crate Keys, and three Huntsman arrows protruding from it, along with a Sandman strapped on top.
When used, it grants 100 extra slots, or two full pages, to the user's in-game backpack. Multiple Backpack Expanders can be used by the same player to obtain a maximum of 3000 slots (60 pages). This means all players can use up to 27 Backpack Expanders, leaving Free-to-Play players at a total of 2750 slots. The remaining 250 slots can be obtained by upgrading to Premium.
December 17, 2010 Patch (Australian Christmas)
- [Undocumented] Added the Backpack Expander.
- Increased the maximum size of backpacks from 1000 to 2000.
- Backpack expanders are on sale for 80% off.
October 20, 2017 Patch (Jungle Inferno Update)
- Increased the maximum number of backpack slots to 2500 (from 2000).
December 21, 2017 Patch #1 (Smissmas 2017)
- Increased the maximum number of backpack slots to 3000 (from 2500).
- Updated the description for the Backpack Expander.