This invention relates to a pipeline assembly especially for offshore installation comprising an inner carrier pipe, a casing and at least one closed-cell and/or solid thermal insulation material layer placed in between the casing and the inner carrier pipe, and the at least one insulation layer being directly or indirectly bonded to at least the casing and the inner carrier pipe. The pipeline assembly has improved bending properties which is achieved as the insulation material layer comprises at least one slit substantially transversely to the longitudinal direction of the pipeline assembly. The slit can be applied as a helical or circumferential cut, enabling the pipeline assembly to be rolled onto a reel or spool which greatly improves the pipeline assembly installation process. Methods of improving the bending properties of such a pipeline assembly are also described.