A noncombustible material is one that isn't capable of igniting and burning. Given the widespread use of composite materials (i.e., a material that is made from a combination of a few different materials, such as a “fiber cement” product), it isn't always clear whether a material is “noncombustible." ASTM E-136 is a standard test procedure that is used to determine if a material qualifies as noncombustible. If in doubt, look to see if this standard is referenced. For example, technical data sheets for fiber cement products, such as Certainteed Weatherboard and James Hardie HardiePlank siding products, state that they qualify as a noncombustible material, according to ASTM E-136.