Developed specifically for controlling flame spread and smoke generation, Synflex 1219 FR [flame retardant] Tubing can be installed in accordance with NFPA, Standard 90A "Installation of Air Conditioning and Ventilation Systems 1985. Synflex FR- Twin can simplify the hook up and routing of any 2-tube, low pressure instrument or control line installation. Identical tubes are held together with a continuous, extruded web, making FR-Twin best suited for push-on barbed fittings. FR- Twin is manufactured from the same flame retardant polyethylene used to make Synflex 1219 "FR" single line tubing. FR-Twin is manufactured from a proprietary UL recognized compound, having a UL-94 V2 flammability classification. In addition to our standard test program of heat aging, ultraviolet light protection, stress crack resistance, and toxic off gassing, Synflex tubing is a listed product with a UL Classification for flame and smoke generation per UL 1820. Tube Identification: One tube is marked with our convenient 1 thru 30 marking system, so if grouped together, tubing pairs are easily distin­guished by cutting both ends at a speci­fied number. Look for UL Classification marking on product.