The definition of porosity is any void or hole in a casting. But this definition does not describe or give direction on the root cause of porosity. Casting porosity can be caused by gas formation or solidification shrinkage while the metal is a liquid. If a casting needs to be pressure tight, then the porosity can allow gas and fluids to seep from the part. In addition, the porosity can weaken the casting. In this blog, we will discuss the difference between gas and shrink porosity, and the best solution to seal porosity.