Soldered fittings, also called "sweat fittings," are used to join copper pipes such as those commonly encountered in some in-wall tub and shower applications. Soldering a pipe joint or "sweating a pipe" is accomplished by heating a copper fitting with a propane torch until the fitting is just hot enough to melt metal solder. The heat draws the solder into the gap between the fitting and pipe to form a water tight seal. Soldering requires some skill and attention to safety, but it creates a strong bond when joining copper pipes. Flexible copper tubing can also be joined with compression fittings or flare fittings (these do not require soldering).