A lining tube of resin-impregnated curable fiber material, which after being pulled in and made to expand within a conduit, is cured from the inside by irradiating with electromagnetic radiation and/or heat. A device for checking the curing through of the fiber material contains a first and second electrical conductor, which extend parallel to one another over a length of the lining tube and arranged between which is a portion in strip form of a reaction resin that has a higher electrical conductivity in the liquid state than in the cured state of the same. A method checks the curing through of the lining tube for the final check on the complete curing through of the reaction resin, the electrical resistance is recorded at two adjacent ends of the first and second electrical conductors and after that the recorded resistance value is compared with a predetermined resistance setpoint value.