A patch (sectional liner) uses the same resin-and-fabric principle as full relining, but targets one defect: a single crack, a displaced joint or one root entry point. A packer carries the resin-wetted patch to the exact spot located by CCTV, inflates, and holds until cured.
Patching is economical when a drain is otherwise sound. Multiple defects spread along a pipe usually tip the balance toward a full-length liner.