A device for the dosing of a dry additive gas into a breathing gas in a ventilator system, the ventilator system including a tubing system connectable by at a distal end to a patient, and has a dosing tube connectable to the tubing system for dosing to the distal end of the tubing system. The dosing tube is composed of a tube section having a moisture permeable contact surface, adapted to interact with moisture from exhaled breathing gas, so the dry additive gas is humidified before dosing to the distal end of the tubing system.