An adhesion-promoting system for a rubber composition, wherein the system comprises a novolac resin prepared by reaction of an aldehyde A1 with a phenolic compound; and an organic manganese salt.

A sound-absorbing material includes an open-cell, filled silicone foam having a density of less than 155 kg/m.sup.3 and a porosity of at least 70%, wherein the silicone foam has an average cell size of less than 2300 micrometers, determined in a direction parallel to the rise direction, and an average cell size of less than 800 micrometers, determined in a direction perpendicular to the rise direction, each determined by optical microscopy.