Closed operator ideals and interpolation

We consider closed operator ideals, which mean operator ideals A whose components A(E, F) are closed subspaces of the space L(E, F). Using interpolation techniques, we obtain general results on products of closed ideals. Furthermore, we investigate which closed ideals A possess the factorization property, i.e., each operator of A factors through a space with the related property “A”. Applications of these results yield the answer to some open questions in ideal theory.