Hats (or Headwear) are items equippable in the 'head' slot of the loadout screen. Valve introduced the first set of 9 hats with the Sniper vs. Spy update. Several major updates have since added additional sets, including hats designed by members of the Team Fortress 2 community.
Hats can be obtained at random through the item drop system, crafting system, Mann Co. Supply Crates, or bought from the Mann Co. Store. Some hats are available to players as a reward for completing in-game achievements, and some hats have been added as promotions for other Steam games and events in the Steam Store, including Left 4 Dead 2, Sam & Max: The Devil's Playhouse, Alien Swarm, Worms Reloaded, Poker Night at the Inventory, Killing Floor, and The Great Steam Treasure Hunt. While it is possible to obtain these hats via trading with other players, there is no way to craft or buy these hats from the Mann Co. Store.
With the release of the Mann-Conomy Update, "unusual" versions of hats have a rare chance of being un-crated when the player opens a Mann Co. Supply Crate. These hats are the same as the original hats, except for an application of 1 of 26 particle effects. A more detailed description of these effects can be found here. Since the update that first added Mann Co. Supply Crates to the game, there have been several new series crates put in the game.
Hats are purely cosmetic, with the exception of the Polycount Pack hats which provide bonuses when worn with their associated item sets.
