One of the special properties of sintered materials is porosity. This is a property which is utilised in the manufacture of sintered filters and self-lubricating bearings, and which makes calibration of sintered components possible.

In most cases porosity has no practical importance. In other cases porosity is undesirable and must therefore be eliminated. 

This is for example the case if the components must be pressure-tight (e.g. when they form part of hydraulic systems) or if the components must be subject to surface treatment where there is a danger that processing fluids may get trapped as a result of the porous properties.

In such cases the pores are sealed. 

This can be done through impregnation with a polymer (plastic), steam treatment or by infiltration with a metal with a lower melting point that that of the actual component.

Plastic impregnation provides the best seal, when a pressure-tightness of up to 20 bar nitrogen is possible. The polymer used is heat resistant up to 200 °C constant.

Only if the component must function at a higher temperature is infiltration with metal used (usually with copper).