The volume node is a core component of the framework and is used by a lot of other nodes such as emitters, constraints, forces to only name a few.
But let's clear up what a volume actually is in Effex. Roughly spoken: a volume defines an inside and an outside.

Think of a plane primitive. This is not a volume because it has no inside. It's just a surface.
A cube on the other hand is a perfect example for a solid volume. It is a closed polygon mesh and you can easily distinguish the inside and the outside of it.

These conditions must be met:
- Closed polygon mesh. No polygon holes. It may work but there is no guarantee it will be correctly detected.
- Resulting from the above point, it has to have an inside and an outside.

The volume is internally encoded into a signed distance field (sdf) which has the property of storing the distances to the nearest surface and therefore is always aware where the surface is.

As the sdf is stored into a special grid inside the volume its resolution depends on the global voxel size of the Effex Scene it is defined in.