Natural fibres are either obtained from plants or animals. Most of the fibres that are obtained from plants are composed of cellulose. We know that plants and animals products are food materials for the moths. Thus the moths feed on plant and animal fibres which are nothing but plant and animal products. Synthetic fibres are man made fibres which are composed of raw materials that are obtained from petroleum. In other words, synthetic fibres are composed of chemicals, on which the moths cannot feed. Hence the natural fibres can be easily attacked by moths whereas synthetic fibres are not easily attacked by moths.