Tape is used in car windows for two reasons. First, sometimes a damage car window needs to be completely replaced, including the strips and moulding that go with it. When this occurs, you can use tape to protect the paint around the window so that less damage is done. Second, when a window is completely broken and is not yet fixed, you can use tape to seal the window shut temporarily while you order a new window to install.
Tape to Protect Car Paint
A new car window, especially a new door window, which is the most like DIY window installation project, can be difficult to install. You will need to remove the entire old window to have enough room to fit the new window in and slide it into place. Examine where your old window was placed. Is there a moulding that goes around the edge of the window frame? If there is, you will need to remove it. It may be glued on, bracketed on, or simply pushed into place and compressed. No matter which way, removing it can easily damage the paint along the sides of the car where the surface and window frame meet.
To avoid this damage, use masking tape and create a barrier all along the window frame, covering all the paint within an inch or two of the window itself. If your moulding has brackets, disengage them and pull it out. If it is glued in--a common procedure--use a small drill to create holes in the glue of the moulding cracks, then use piano wire or a similar wire to saw through the glue and remove the moulding completely. This will give you enough room to remove the old piece of glass.
Tape Broken Window Openings
If you cannot immediately repair a side window in your car, seal it until such time as the repair can be made. Plastic is the most popular and probably most dependable choice. Use as heavy duty plastic as you have available. A garbage bag can work, but an old tarp that can be cut apart is even better. Since you want the plastic to stick in place and creating a dependable, weatherproof seal, avoid using masking tape and switch to duct tape instead.
Cut the plastic into the shape that you need, making it several inches larger than the window frame itself. Use two or three sections of duct tape to bond the plastic to the top and bottom of the window, pulling the plastic taut as you do so. You want as little give in the temporary barrier as possible. Once the top and bottom ends are in place, run long strips of duct tape around the entire window frame, at least two of them. Leave no spot open and apply gentle pressure to the duct tape to ensure it has formed a complete seal.