The friction of a sector determines how easy it is to change the momentum of things that touch the floor of the sector. Friction is defined as a floating point number in range 0 to 1.0. The lower the number, the larger the friction seems. Each game_tic (35 times per second) the momentum of the mobjs that touch the floor of the sector is multiplied by the friction value. This means if the friction is set to one, the momentum of the things inside the sector won't decrease at all.

Kind Value Original Hex
Standard friction 0.90625 0xE800
Heretic ice friction 0.97265625 0xF900

As friction decreases (the value is nearing one), it becomes harder and harder to change the momentum of things, i.e. to accelerate or decelerate.

Example

Sector Type {
    ID = 5009
    Comment = "Half friction"
    Flags = friction
    Friction = 0.5
}

This will enable friction in the sector and change it to the desired value (Friction).