Fiber cement consists of fibrous, non-flammable materials, such as wood pulp mixed with Portland cement, water and silica or fly ash. By virtue of its physical properties, fiber cement siding is less susceptible to common environmental threats (such as fire, heat or moisture) than traditional wood cladding.
In encounters with fire, wood siding quickly becomes fuel and vinyl siding will melt. Fiber cement siding, on the other hand, will resist combustion. Organizations such as the ASTM, the National Fire Protection Association, and the Canada/Unlimited Liability Corporation (CAN/ULC) have developed an array of tests utilized by manufacturers and governments to measure ignition resistance, combustibility and flame spread in building/wall products. These tests allow manufacturers to prove that fiber cement may be safely used with wall assemblies that have been rated fire-resistant.