Rubber particles having textile and/or metallic inclusions are treated by first placing the particles on a support surface and then pressing the particles against the support surface in a direction transverse to the support surface with a surface of a press body exerting a pressure of in excess of 10 kg/cm.sup.2 without contacting the surfaces with each other. Both of the surfaces are nonsmooth. In accordance with the invention the support surface and the press body are relatively displaced in a direction generally parallel to the support surface to subject the particles to shear.