Difference in UDTs?

Feel free to howl me down here but I was wondering if anyone who has tried difference UDTs (Voit duck feet model) has notice any variation in the flex?

I have a matt black pair in XXL for winter when I need booties and recently bought an XL pair for warmer water here in Victoria, OZ.

The XLs were marbled blue and feel like they have a lot more flex in them than the matt black pair.

Both are unmodified and have been used with mats or handplane, admittedly sparingly as I spend most water time on a board.

Neither pair is more than 2 years old.

Could the perceived variation in flex be due to the size difference? Any difference in rubber compound or am I just imagining it?

cheers

I have both models as well.

You are correct in your assumption.

The matte black is slightly stiffer then the marbled blue (or red) models.