This attribute provides the opportunity to add multiple categories to your item.
The 'product type' attribute is strongly recommended for all items. If your item refers to more than one category you can add multiple product type attribute values. Also use this attribute in case you would like to add your own categories in addition to the required attribute Google product category.
You can add multiple product types for your item if it seems sensible. To do that just separate the product types with a comma in a tab-delimited datafeed file or include multiple
It is recommended to include full category strings to your items. That means if you want to classify your item as a Mobile Phone the full string would be 'Electronics > Communications > Telephony > Mobile Phones'. As you can see categories have to be separated by '>' including a space before and after the symbol. You can find a list of all product categories here.