Material with variant

Dear gurus,

this is my scenario: I would like to buy through PO 4 different sizes of the same T-shirt from the same vendor.

I would like to use same material code for the 4 different sizes, can you help me understanding how to proceed?

I tried creating a KMAT material associated with a class Type 300 and 4 characteristics but when I put the material into PO I can't distinguish between sizes. Any suggestion?

Thank you in advance, warm regards,

Fuffo