On Google's Product Feed Specification, regarding variants, it says:
We define variants as a group of identical products that only differ by the attributes ‘color’, ‘material’, ‘pattern’, or ‘size’.
But what if I have a products that actually differ by other attributes? For example, I could have variants that differ by "Color", "Surface" and "Volume". So there could be two variants with the same color, but different surfaces and volumes. Would Google Merchant see these as duplicates?
From what it seems, I have no way of specifying variants like that...
variants cannot be specified by custom attributes.
surface might be a material or pattern depending on the item details -- generally, if the surface can be differentiated by sight, use pattern; if surface can be differentiated by touch or what the item is made of, use material.
volume can be a size.
the item's size can be complex -- condense the information whenever possible; the item's pattern can be a graphic or pattern;
simply be certain the value is accurate, can be understood by users, and has a different combination of variant values for all items in the variant group.
if the information does not apply, leave the value blank (empty).
for example --
size,material,pattern,color,item_group_id
1000 mm x 600 mm x 355 mm,stainless steel,,,gid1
1500 mm x 600 mm x 355 mm,stainless steel,,,gid1
1700 mm x 1200 mm,plastic,hemispheres,green,gid2
1700 mm x 1200 mm,plastic,spheres,green,gid2
42 gallons,steel,,,black,gid3
200 mm x 200 mm,vinyl,notre dame,blue/gold,gid4
200 mm x 200 mm,vinyl,yankees,white/blue,gid4
5 mm,,,,gid5
6 mm,,,,gid5
a size value would be all that's needed if size alone is sufficient to specify a unique combination for all items within that variant group.
each variant group must have an identical item_group_id value and a unique combination of valid variant values per item -- otherwise, google will classify items as duplicates, and is grounds for removing all items, disapproval, or suspension.
if only color is submitted and the variants are all the same color, then the variants cannot be submitted -- without risking all items being removed, disapproval, or suspension.
variants are not required to be submitted -- alternatively, simply submit only the one item featured on the landing-page.
also, the website must have a landing-page with a matching price of the variant.