product_packaging for general variant subarticle

[Damenm]

I have subarticles where only the weight is changing: 100 gr, 200 gr, etc.
When I enter this as  product weight, I only get the digits in the dropdown list: 100, 200 etc.
I want it including the units, So I thought I enter is as "product_packaging" but this variable is not selectable as variant subarticle.
How to incorporate this one