A ProductGroup represents a group of [Product](https://schema.org/Product)s that vary only in certain well-described ways, such as by [size](https://schema.org/size), [color](https://schema.org/color), [material](https://schema.org/material) etc. While a ProductGroup itself is not directly offered for sale, the various varying products that it represents can be. The ProductGroup serves as a prototype or template, standing in for all of the products who have an [isVariantOf](https://schema.org/isVariantOf) relationship to it. As such, properties (including additional types) can be applied to the ProductGroup to represent characteristics shared by each of the (possibly very many) variants. Properties that reference a ProductGroup are not included in this mechanism; neither are the following specific properties [variesBy](https://schema.org/variesBy), [hasVariant](https://schema.org/hasVariant), [url](https://schema.org/url).