A variant of the static spark hypothesis, presented by Addison Bain, is that a spark between inadequately grounded fabric cover segments of the "Hindenburg" itself started the fire, and that the spark had ignited the "highly flammable" outer skin. The "Hindenburg" had a cotton skin covered with a finish known as "dope". It is a common term for a plasticised lacquer that provides stiffness, protection, and a lightweight, airtight seal to woven fabrics. In its liquid forms, dope is highly flammable, but the flammability of dry dope depends upon its base constituents, with, for example, butyrate dope being far less flammable than cellulose nitrate. Proponents of this hypothesis claim that when the mooring line touched the ground, a resulting spark could have ignited the dope in the skin.