A liner is a seamless pipe sleeve that is installed inside of an existing pipe. The sleeve is made of felt with a plastic coating on one side. The felt portion of the liner is saturated with an epoxy resin. The liner is then inverted into the existing pipe (if you can picture unrolling a pair of socks) so that the plastic coating is in the inside of the pipe and resin is on the outside against the existing pipe wall. A calibration tube is then inverted (like a long balloon) and inflated to hold the liner open against the existing pipe. Steam is used to cure the resin. The end product is a hardened pipe moulded to the inside of the existing pipe.
The liner is about 3.5mm thick so in total it reduces the inside size of the pipe by about 7mm. This reduction in size will not have a negative affect on the flow. As the new liner is smooth and seamless (no joints) it will instead increase the flow rate. A four inch service pipe is oversized for regular residential use so there will be no issues caused by the minor reduction to the inside diameter (Pipe ID).
Thuro is a Perma-Liner Certified installer and we have installed hundreds of liners in Calgary and Southern Alberta. A CIPP liner is a permanent repair. It will extend the life of the existing pipe by at least a full lifetime. Current third-party testing through ASTM shows a life expectancy of 50 + years, however this number grows each year. Lining was first invented in 1971, and Thuro was actually the first company in Calgary to utilize this trenchless technology. We have been installing liners for 25 years and none of our liners have failed following a successful installation.