What is the liquid that comes out of air duster (canned air)?

Most duster contain refrigerant that is liquid when held under pressure. The goal of duster is to spray the vapor not the liquid, so the valving is designed to capture the vapor from the top of the can. When you shake a can, turn it, or flip it upside-down, you can introduce the liquid refrigerant to the mix. Careful, because that is cold enough to cause frost bite and damage sensitive electronics. Vortex 360 (part #1697-8S) is designed to spray upside-down without expelling liquid refrigerant.