Incorporeal

This creature is insubstantial and weightless, able to pass through solid objects such as walls and weapons.
Incorporeal creatures gain the Hoverer (6) trait and a +30 bonus on Stealth tests due to their ability to merge with objects and nearly silent movement.
An Incorporeal creature is also immune to normal weapons, which simply pass ineffectually through its body.
Daemons, psychic powers, Warp creatures, other Incorporeal creatures, and opponents armed with force weapons can all injure an Incorporeal creature normally. An Incorporeal creature cannot usually affect the mortal world, and thus cannot damage normal opponents unless it has a suitable special ability or talent.
Certain devices can keep these creatures at bay, though, most notably a Void Shield or a spaceship’s Gellar Field, which acts as an impenetrable barrier to them.