For the purposes of this post, we'll be addressing fiberglass batt insulation. There are multiple types and manufacturers of fiberglass insulation. Some have vapor barriers, no vapor barrier, vapor barriers that are non-combustible and vapor barriers that are extremely combustible.
During a recent inspection we found an extremely well insulated attic, however the insulation was installed improperly with the combustible vapor barrier left exposed. OEM warning labels were clearly printed in English on each section of the subject insulation. This highly flammable paper barrier can act like kindling for a fire and the vapor barrier rendered useless because its not facing the interior of the structure. Any number of ignition sources can exist in a structures attic and if the conditions are just right, fire can be the result.