There is no other material, either manmade or natural, with all the properties and characteristics that are unique as cork: light weight, soft, rot resistant, compressible and recoverable, expandable, fire resistant in its natural state, impermeable, and buoyant. There is no other material, either manmade or natural, with all the properties and characteristics that are unique as cork: light weight, soft, rot resistant, compressible and recoverable, expandable, fire resistant in its natural state, impermeable, and buoyant.