If steam contains 10% water by mass, it's said to be 90% dry, or have a dryness fraction of 0.9. The steam dryness fraction is used to quantify the amount of water within steam. Unless a superheater is used, this will cause the steam supply to become partially wet (wet steam) from the added liquid. Did you know that boilers do not generate 100% saturated steam (dry steam)? When a steam boiler heats up water, bubbles breaking through the water surface will pull tiny water droplets in with the steam.
