In this category are close-fit linings in which the plastic lining pipe (typically polyethylene) is sized to fit tightly inside the existing host pipe. To allow the insertion of the lining pipe, the lining pipe is reduced in diameter just prior to installation, pulled into place and then expanded again within the host pipe to achieve the close fit. The swage lining method pulls the pipe through a reducer die and keeps the pipe under high tension while it is being installed. When the tension is released, the pipe expands as it tries to return to its original shape – locking the liner pipe tightly inside the host pipe. In the rolldown process, the pipe is forced through a set of rollers that both reduces the outside diameter of the liner pipe and increases its wall thickness. The rolldown process leaves the pipe in a more stable condition in terms of its reduced diameter during the installation process. Once the liner pipe is in position, the geometry reversion is accomplished using internal pressure.