Abstract: The invention relates to a method of manufacturing a seal for a roller bearing, for instance a ball bearing. The seal according to the invention is formed from a thermoplastic polymer-containing material which is subsequently cross-linked under the influence of radiation, for example .beta.-radiation. This allows the use of seals manufactured according to the invention at near or even above the melting point of the non-cross-linked thermoplastic polymer being employed. Due to the invention a large number of cheap polymeric materials have become suitable for the manufacture of seals, and due to the cross-linking the swelling caused by lubricants can be reduced considerably.