The Basic Principle of insultion is an air barrier. Many Natural Materials can insulate, but they can present Problems by moldering or burning. Mineral Wools are fire resistant. Fire Retardant foams such as Icynene are available that have Passed the Test of fire. Foam insulation is Superior to other forms of insulation in many ways. The benefits of insulation can seen in the Growworld Module Project, which uses passive solar energy and can maintain indoor gardens even in cold temps.