The ProFlex line of universal tubing is a proprietary Fluoroelastomer (FKM) tubing that will NEVER harden. ProFlex has been designed and tested to be impervious to gas, glow, diesel, and smoke oil. The thin walls allow maximum flexibility without kinking. Three lengths, 6" tank replumb kits, 2' length, and 10' length, available in two different sizes, Standard and Large. ProFlex Standard (S211 & S212) has a 3/32" ID which is exactly the same ID as the silicone fuel line that comes with every tank. It is designed to fit 1/8" Brass tubing as well as standard size fuel fittings.
ProFlex Large (S215 and S216) has a 5/32" ID which is designed to fit 3/16" brass tubing as well as large size fuel fittings. In order to use the large size ProFLex in a tank you must replace the brass tubes and klunk to 3/16".
Sullivan designed the ProFlex fuel line with a US chemist and rubber compounder to develop a proprietary formula of FKM (Fluoroelastomer) that is chemically resistant to gasoline and ethanol which is what causes Tygon tubing to harden and deteriorate. With the help of an experienced US extruder, ProFlex has a thinner wall than commonly found on the Tygon that is used today. The thinner wall allows for more flexibility, lighter weight and easier attachment to tubing and fittings used in the RC industry.