Abstract: Two-shell flat casings 10, 11 having an inner receptacle for low-viscosity gel precursor 13 which sets (preferably by curing) in receptacle and has displaceable wall 18 which is displaced by camming action 24,25 on closing together of the shells to allow the wires or other enclosed objects to extend out of the casing through space previously occupied by the displaced wall. Polysiloxane gels and glass-filled polypropylene casings are preferred, preferably molded as a single hinged piece with a hinge and frangible retaining webs for the displaceable wall. The design is well suited to high-volume automated production, e.g. for the automotive wiring market.