An assembly comprising: (i) a containing means for molten polymer; (ii) apparatus (117,124;200) for injecting a fluid formulation into molten polymer contained in the containing means, wherein said apparatus is secured relative to the containing means; (iii) wherein said apparatus includes an injection device (117;217) for injecting fluid formulation into molten polymer contained in the containing means; (iv) wherein said injection device comprises a conduit (117;217) arranged to deliver fluid formulation into molten polymer in the containing means and a cooling fluid passageway associated with the conduit, said cooling fluid passageway (148;300) being arranged to contain a cooling fluid which is arranged, in use, to cool the conduit and/or a fluid formulation present therewithin; characterised in that: one wall W1 of the said cooling fluid passageway is defined, at least in part, by said conduit arranged to deliver fluid formulation into molten polymer, wherein wall W1 defines an internal wall of the cooling fluid passageway; said conduit includes a wall having a first surface which is an internal surface of the conduit and is arranged to contact fluid formulation as it passes through the conduit prior to injection of the fluid formulation into molten polymer and said conduit includes a second surface (147; 294) which is an external surface of the conduit and/or faces outwardly and does not contact the fluid formulation as it passes through the conduit, wherein the arrangement is such that cooling fluid in the cooling fluid passageway in use directly contacts said second surface of said wall of said conduit; a wall W2 of the cooling fluid passageway extends around the conduit and is arranged to contact cooling fluid in use, wherein wall W2 is part of a securement device (124; 224) by means of which the conduit of said injection device is secured in position; and said securement device comprises a screw-threaded region (150; 250) which is arranged to screw-threadedly engage the containing means. (i) a containing means for molten polymer; (ii) apparatus (117,124;200) for injecting a fluid formulation into molten polymer contained in the containing means, wherein said apparatus is secured relative to the containing means; (iii) wherein said apparatus includes an injection device (117;217) for injecting fluid formulation into molten polymer contained in the containing means; (iv) wherein said injection device comprises a conduit (117;217) arranged to deliver fluid formulation into molten polymer in the containing means and a cooling fluid passageway associated with the conduit, said cooling fluid passageway (148;300) being arranged to contain a cooling fluid which is arranged, in use, to cool the conduit and/or a fluid formulation present therewithin; one wall W1 of the said cooling fluid passageway is defined, at least in part, by said conduit arranged to deliver fluid formulation into molten polymer, wherein wall W1 defines an internal wall of the cooling fluid passageway; said conduit includes a wall having a first surface which is an internal surface of the conduit and is arranged to contact fluid formulation as it passes through the conduit prior to injection of the fluid formulation into molten polymer and said conduit includes a second surface (147; 294) which is an external surface of the conduit and/or faces outwardly and does not contact the fluid formulation as it passes through the conduit, wherein the arrangement is such that cooling fluid in the cooling fluid passageway in use directly contacts said second surface of said wall of said conduit; a wall W2 of the cooling fluid passageway extends around the conduit and is arranged to contact cooling fluid in use, wherein wall W2 is part of a securement device (124; 224) by means of which the conduit of said injection device is secured in position; and said securement device comprises a screw-threaded region (150; 250) which is arranged to screw-threadedly engage the containing means.