The quality of the sand that is used also greatly affects the quality of the casting and is usually described by the following five measures:
Strength – Ability of the sand to maintain its shape.
Permeability – Ability to allow venting of trapped gasses through the sand. A higher permeability can reduce the porosity of the mold, but a lower permeability can result in a better surface finish.
Thermal Stability – Ability to resist damage, such as cracking, from the heat of the molten metal
Collapsibility – Ability of the sand to collapse, or more accurately compress, during solidification of the casting. If the sand cannot compress, then the casting will not be able to shrink freely in the mold and can result in cracking
Reusability – Ability of the sand to be reused for future sand molds
