Such things as moss, feathers, cotton, wool, sawdust, corn cobs, and cork have relatively good insulating properties and as a result they have found their way into more than a few walls and attics. Unfortunately, a material must have more than good insulating ability to be a good insulation. There are many people who are allergic to natural items such as feathers, wool, etc. Also, natural substances make good nesting materials for small animals and insects. They may also provide food for these unwanted residents.
Mold growth can also be a problem.
Mold can not only be undesirable to allergy sufferers, but it can be detrimental to the health of the house because when wood rots it is being eaten by a fungus. Unless heavily treated with potentially toxic chemicals, these products can also be very flammable. Because of the drawbacks to using natural materials, most insulation producers today rely on man-made concoctions. While these manufactured products are widely used, and believed to be nontoxic, there are some negative health effects that the concerned homeowner should be aware of. The most common way of comparing insulations is by their Rvalue.