Nut shells are the hard outer coverings that protect the seeds of various types of nuts, such as walnuts, almonds, and hazelnuts. These shells serve as a natural barrier against pests and environmental factors, ensuring the seeds inside remain safe until they are ready to germinate or be consumed. The composition of nut shells varies by species but is generally made of lignin and cellulose, making them tough and durable. Once the nut is harvested, the shell can be discarded or repurposed, as some people use crushed shells for gardening or as a natural mulch to improve soil quality.