Preformed pipe insulation is made of polystyrene and looks like long, flexible tubing. It is installed on pipes outside a wall to protect them from freezing temperatures in the winter. Pipe insulation has a basic design that even homeowners can install themselves. However, installation can be tricky when you have two pipes that meet at 90 degrees and form a "T" shape. In these instances, multiple pieces of insulation must be used.
Hold a piece of the pipe insulation up to the horizontal pipe and align the end of it with the end of the pipe. Place your finger at the location where the tubing must be cut to size.
Move the insulation tube to a flat work surface and cut through it at the location of your finger using a sharp utility knife.
Pick up the insulation and find the slit that runs along the length. Hold the slit open with your fingers and slip the tube around the horizontal pipe. There will be a gap in the tubing where the vertical pipe emerges from the horizontal pipe, but that is fine.
Peel off the two pieces of white paper from inside the slit and release the tube, allowing it to close around the pipe. Press the tube together with your hand to secure the inner adhesive. When you reach the "Tee" section, press the tube closed as much as possible.
Insert a utility knife into the tube directly beside the vertical pipe, or the "tee." Cut down by approximately 1/2 inch. Make another cut on the other side of the vertical pipe that is also 1/2-inch long. Cut the tab off between the two lines so that you now have a small square notch cut in the tube. Push it up around the vertical pipe.
Cut another piece of tubing to fit the length of the vertical pipe. At one end of the tube, use the knife to create a concave depression instead of a straight cut. The concave area should be toward the inside of the tube, producing the appearance of an open fish's mouth.
Place the tube onto the vertical pipe with the concave section facing downward. Peel off the inner tape and press the tube together with your fingers.