I remember the directions saying to remove it, so that is what we have done when using both the bubbles mask with our older daughter and the infant mask with the younger one.
OK. I just looked up the directions.....it says to 'remove the inspiratory valve cap from the nebulizer insert' for the bubbles the fish mask, but to leave it in place on the baby masks! I guess we have been doing Isabella's wrong all this time!! Eeeek! After Isabella was dianosed and started using the nebulizer, I guess I didn't go back and reread the directions. I just assumed the baby mask would be the same as the bubbles mask.
Julie