An insertion system for the weft yarn of a jet loom, comprising a jet insertion device in the jet loom for withdrawing the weft yarn and for transporting the same into a shed, and a weft-yarn storage, supply and measuring device arranged upstream of the jet insertion device. The weft-yarn storage, supply and measuring device including a weft-yarn stopping and releasing device which is controllable in response to a weaving cycle. The insertion system also includes a mechanical weft-yarn slip conveyor arranged in the yarn path of the weft-yarn stopping and releasing device relative to the jet insertion device, which comprises at least on conveyor roller rotating in the insertion direction of the weft yarn at a faster circumferential speed than the maximum weft-yarn insertion speed and can be deactivated while the conveyor roller is rotating during the insertion process. With the slip conveyor activated, the weft yarn surrounds at least a partial region of the circumferential surface of the roller and can be acted upon with a slip conveyor force determined by the withdrawal tension in the weft yarn. The insertion system further includes a yarn brake arranged in the yarn path at the slip conveyor or downstream of the slip conveyor, which can be engaged in response to the weaving cycle.