The term "porosity" simply refers to the presence of microscopic pores in the Tungsten carbide/Cobalt matrix. If the total porosity or if the volume of the largest pores present exceed a critical value, then the properties of the material can be affected.

Typical porosity is rated in three different types.
A-type refers to pores less the 10mirons in diameter
B-type refers to pores between 10microns and 40microns
C-type is based on excess carbon content and is addressed below

And at different levels according to the estimated total volume of porosity in the sample.

For example, a sample rated at A-02 B-00 C-00 porosity has pores less then 10microns in diameter with a total pore volume of .02% of the sample. A rating of A-04 B-02 C-00 indicates a total pore volume of .06% for pores less then 10microns across, .02% for pores between 10microns and 40microns and an overall pore volume of .08%.