Electrical cable jacket material is usually constructed of flexible plastic which will burn. The fire hazard of grouped cables can be significant.[3] Cables jacketing materials can be formulated to prevent fire spread[4] (see Mineral-insulated copper-clad cable). Alternately, fire spread amongst combustible cables can be prevented by the application of fire retardant coatings directly on the cable exterior,[5] or the fire threat can be isolated by the installation of boxes constructed of noncombustible materials around the bulk cable installation.