Coatings for protecting and insulating fluid and/or gas transport conduits, such as off-shore oil and gas pipelines operating at temperatures of up to 100° C. in water depths above 1,000 meters. The outer surface of the conduit is provided with at least one layer of thermal insulation comprising polystyrene or styrene-based thermoplastic, having low thermal conductivity, high thermal softening point, high compressive strength and high compressive creep resistance.