Abstract: A flexible joint is disclosed which comprises a first rigid wall portion, a second rigid wall portion, a flexible wall portion extending between the first and second rigid wall portions, the three wall portions defining a longitudinal passage through the joint and being arranged along the length of the passage, a sleeve secured at one end to the first rigid wall portion and extending through the passage so as to overlap the second rigid wall portion, the sleeve being spaced from the flexible wall portion and free to move relative to the second rigid wall portion. In a preferred embodiment, a layer of insulating material is provided on a surface of the sleeve while leaving the space between the sleeve and the flexible wall portion to be occupied by process fluid when in use. In another embodiment, the length of the portion of the sleeve overlapping the second rigid wall portion is at least five times the distance of the sleeve from the second rigid wall portion, as measured perpendicular to the sleeve.