Mobile Flex BB-100 Bottom Board Underbelly Wrap, 48" x 100ft, with a Lumintrail Keychain Light Mobile Flex is a special bottom closure, woven from black high-density polyethylene and extrusion coated with a continuous layer of low density polyethylene. The material is uniform in quality with no weak spots. Its beach puncture resistance is more than five times the minimum established by HUD! Staple hold out is excellent. Penetrations and cuts will not spread and can be easily patched using our Flex-Mend tape. MOISTURE- Mobile flex is totally impervious to water. Its strength cannot be adversely affected by moisture. Because of its black polyethylene coating, Mobile Flex qualifies as a vapor barrier. Technical report #19757 from Chicago Paper Testing Laboratory, Inc., reports the material to have an average perm rating of 0.037. DURABILITY- Mobile Flex is produced from a material that has been tested for durability and weatherability. After seven years of continuous, direct exposure to the elements in Arizona, the material retained 70% of its strength. The tapes and coatings are both chemically tested to ensure maximum performance. FLAMMABILITY- Mobile Flex is classified by Underwriters Laboratories, Inc., as to surface burning characteristics. Mobile Flex tested out to zero flame spread and zero smoke developed. The tests were conducted in accordance with UL Standard Test Method for Surface Burning Characteristics of Building Materials, UL 723.