A resin impregnated felt tube made of polyester, fiberglass cloth, spread tow carbon fiber or another resin-impregnable substance, is inserted or pulled through a damaged pipe. It is usually done from the upstream access point (manhole or excavation). It is possible to insert the liner upstream (e.g. from the downstream access point) but this carries greater risk. It is possible to install a liner from the downstream access point, upstream to a blind end; however, this carries the highest risk of all the CIPP installation methods. CIPP is considered a trenchless technology. Little to no digging is involved in this trenchless process, making for a potentially more cost-effective and less disruptive method than traditional "dig and replace" pipe repair methods. The liner can be inserted using water or air pressure. The pressure required for insertion can be generated using pressure vessels, scaffolds or a "chip unit". Hot water or steam can be used to accelerate the curing rate of the resin.  If a fiberglass tube is used, the curing of the resin can be triggered though the use of UV light introduced into the tube.  As the resin cures, it forms a tight-fitting, joint less and corrosion-resistant replacement pipe. Service laterals are restored internally with robotically controlled cutting devices called cutters in the larger-diameter pipe. Smaller diameters (100 mm) can be opened remotely using smaller cutters designed for small diameter pipe. The service lateral connection can be sealed with specially designed CIPP materials, sometimes referred to as a top-hat. The resin used is typically polyester for mainline lining and epoxy for lateral lines. Since all resins shrink (epoxy resins shrink far less than poly and vinyl ester versions) and it is impossible to bond to a sewer that has fats, oils, and grease an annular space exists between the new CIPP liner and the host pipe. The annular space exists in all installations just some are larger than others and depending on the severity may need additional rehabilitation. There are multiple ways to prevent water from tracking in the annular space and entering back into the waste stream including: water swelling material (hydrophilic), lining of the entire connection and host pipe with a continuous repair (YT repair) gaskets, and point repairs placed at the ends of the host pipe.