Balaclava
The Balaclava is a black three-hole mask that is a wearable item in GTA IV. It can be seen worn by Niko, Packie, Derrick and Michael in the mission Three Leaf Clover and becomes available in Niko's wardrobe afterward. Altough a mask it is categorized as a hat. Unlike a hat the Balaclava will not disappear when Niko enters a car or when a motorcycle helmet is used (over the balaclava).
It is also available in the player's skin in the multi-player mode in The Lost and Damned in different colors.
On the PC version, there are modifications to change the color of the mask and some say that it's possible to change it's design and have it like a hat. It is also possible to make it like an army mask.