Microporous “sponge” gaskets are sealing materials with a foam, sponge-like structure, i.e. with many small air cavities inside. This type of structure gives them completely different properties than compact (solid) rubbers.

Main features of microporous (sponge) seals:

Low density – are light and soft.
Excellent compressibility – easy to squeeze and return to their original shape when released.
Good sealing at low pressures – Suitable where high tightening force cannot be used.
Insulating properties – Thermal and acoustic insulation is often better than compact rubber.
Resistance by material – can be EPDM, silicone, neoprene, NR, etc.; properties depend on the rubber itself.

They are produced either:

by chemical foaming during vulcanisation (a blowing agent is added to the mixture),
mechanical foamingwhere gas is introduced into the polymer during mixing.

The result is a structure similar to sponge – from fine microcells to coarser pores, depending on the type of product.