Refers to the proportion of voids in relation to the total volume of the material. Open porosity is the term used when the pores are interconnected. This usually occurs at a total porosity of >30%. Closed porosity is when the pores are not interconnected.

Especially for metallic sintering, porosity is an important parameter for the service life and stiffness of the material. The lower the porosity, the higher the strength, but also the modulus of elasticity of the joint. The greater the porosity, on the other hand, the greater the reduction in strength and stiffness. As high strength and low stiffness are required for optimum thermal shock resistance of the components, there is an optimum porosity for the sintered layer. This also depends on the overall structure and its residual stresses. The porosity can be adjusted during metallic sintering by the sintering pressure.