Clear PVC tubing is easily inspected and is therefore best for test applications where a possibility of fluid entering the tubing exists. Rubber tubing has less tendency to kink in storage and occupies less space, thus is best for portable work. Aluminum tubing is recommended for permanent installations. Flexible double column tubing is used with Mark II Manometers and the Wind Speed Indicator. Norprene® tubing is useful in a wide range of temperatures from -75 to 275°F (-60 to 135°C)ａnd will not weaken after long term exposure to heat and ozone. Flexible colored vinyl tubing is quickly distinguishable in applications where more than one line is required aiding installation. Black plenum fire retardent polyethylene tubing meets NFPA standard 90A for installation in air-conditioning and ventilating plenum spaces; also used in building automation systems.