This is a read-only property that describes the Enum/Material the Humanoid is currently standing on.
It works with both regular BasePart|Parts and Terrain voxels.

The code sample below demonstrates how to listen to when this property changes using Instance/GetPropertyChangedSignal. When the material the humanoid is standing on changes, it will print a message indicating the new material being stood on.

local Humanoid = route.to.humanoid

Humanoid:GetPropertyChangedSignal("FloorMaterial"):Connect(function()
    print("New value for FloorMaterial: " .. tostring(Humanoid.FloorMaterial))
end)

Caveats

• When the Humanoid is not standing on a floor, the value of this property will be set to Air.
  • This occurs because Enum properties cannot have an empty value.
  • This can cause some confusion if a part has its material is set to Air, though in practice, parts are not supposed to use that material in the first place.
• The Humanoid|Humanoid's character model must be able to collide with the floor, or else it will not be detected.
  • You cannot test if the Humanoid is swimming with this property. You should instead use the Humanoid|Humanoid's Humanoid/GetState function.