What is the difference between porosity and permeability?
The easiest way to understand these terms is with an illustration. Think of a sponge or a Swiss cheese. These things consist of a block of solid material that has a number of gas bubbles trapped in it. If you cut into it, those bubbles look like holes. If there are enough bubbles they can interconnect to form channels. Permeability has to do partially with the size of the bubbles but more specifically with how well they are connected to allow flow. If they are well connected the permeability is high and fluid will flow through easily. Of course, for the same degree of connectedness, larger channels will permit flow more readily than smaller ones. If the bubbles are very small or if they are poorly connected, the permeability will be low and fluid will not flow through easily. Porosity simply tells you how much volume is solid and how much is bubbles. High porosity means more air or space and low porosity means less. Of course, higher porosity also means lower mechanical strength. That
