Cork is the outer bark of an evergreen oak tree that grows around the Mediterranean Sea. It is generally ground up after it is removed from the tree and then processed into sheets. It will retain its light brown color if a synthetic binding agent is used to hold the granules together. This synthetic resin could bother sensitive people. It may contain phenol or formaldehyde resins.
Some cork is processed without a binder being added.
By steam baking the granules in a mold, the natural resins from the cork act to bind it together. Steam baked cork has a somewhat burnt smell and is dark brown in color. While the burnt odor will dissipate with time, some individuals may find the aroma offensive. For them, an easy solution would be to use the virgin cork granules directly from the tree. This can easily be poured in place in areas such as open attics.