Copper pipe is used both by plumbers and for air conditioning (ACR), and the two fields have different ways of sizing the pipe. There are two basic types of copper pipe or tubing: rigid and flexible. Rigid pipe, usually installed in new homes, makes a neater installation, but it is much more difficult to install than soft, flexible copper pipe. Flexible copper pipe is best for repair work since it can be run around obstacles without connections or cuts. Copper pipes which are widely used in the refrigerator industry can sometimes work in high humidity atmospheres and in aggressive conditions which can produce dangerous corrosion phenomena of the pipes.