item_group_id
item_group_id is a shared value you put on every variant of the same product so the channel knows that, for example, a shirt in five sizes and three colors is one product with fifteen variants.
When a product comes in multiple variants, each size or color is its own row in the feed with its own unique id. The item_group_id is what links those rows together. Every variant of the same base product shares the same item_group_id, while keeping the variant attributes (size, color, material, pattern) different.
This matters because it lets channels group variants intelligently. Shoppers can switch between colors or sizes inside a single listing, and the channel avoids showing the same product fifteen times as if it were fifteen unrelated items. It also keeps reporting and bidding cleaner.
In the feed, all variant rows carry the same item_group_id plus their own distinguishing attributes. A frequent mistake is leaving it blank (so variants look like separate products) or reusing the same value across genuinely different products (so unrelated items get merged).
MartechFlow can derive item_group_id from a field in your source data, such as a parent product ID, and apply it across all variant rows automatically, so grouping stays consistent every time the feed refreshes.