In climates where temperatures drop below freezing more often then not, insulation is a necessity, not a luxury.
Before now, the only way to insulate pipe was to cut sheets of insulation, then attempt to fit them around the pipe. When back-filling, there was no guarantee that shifting soil and rocks would not move or collapse the insulation, thus allowing the cold to infiltrate the system.
Insulated PVC pipe, using an application of urethane foam to surround PVC pipe and encasing this in a polyethylene sleeve, forms a "single unit" insulated water / sewer line. This virtually eliminates the need to re-dig lines and correct slipped insulation... saving time and money.
The PVC and urethane foam used in developing insulated PVC has been ASTM approved (ASTM numbers are available upon request). Schedules of PVC used, R-values, and inside and outside diameters are demonstrated in the grid here