It is oil based modelling material that never dries out, shrinks, or hardens after being left out in the air. It can be used over and over again. No mould or fungus can form on the clay. Therefore, no preservatives are added, making it totally safe for children. Our clay is non-toxic, although we do not recommend eating, in the case of ingestion, a child will digest it without any harm. Its shelf life is approximately 3 years.