Method of after-foaming a mixture of a foam and a resin solution

A method of after-foaming a mixture containing a foam and a urea-formaldehyde resin solution, wherein the foam component is brought into contact with the resin component by means of a suction action, comprising directing said resin solution to a mixing chamber through an inner pipe and simultaneously directing a foam to said chamber through a concentric space defined by an outer pipe and said inner pipe, whereby an after-foaming is produced by means of the vacuum produced by said suction action and by superfluous gas present.