Round Hole Duct, 4 Inches x 4 Inches x 6 Feet, Light Gray, Base and covers sold separately, Made of lead-free PVC, UL Recognized continuous use temperatures up to 122 Degrees F (50 Degrees C), UL94 Flammability Rating of V-0, Provided with mounting holes, Conforms with NFPA 79-2007 section 13.3.1 requirement for flame retardant material.