<p>An elastic fiber of a mixture containing a copolyether ester or a copolyester ester and a chemically crosslinked rubber, which fiber has a permanent elongation after 100% stretching of at most 9% and an elongation at break of at least 450% and a process for producing an elastic fiber comprising the melt spinning of a mixture of a copolyether ester or a copolyester ester and a rubber to form a fiber, in which the rubber is completely or almost completely crosslinked at the moment the fiber is formed, and are disclosed.</p>
