what is the diffarence in the foam tyres for the mardave ie the numbers, i was wondering which is the softer lower numbers or higher?

there all a bit mixed up now, i know v53's are really really soft, and wear fast, but make for good tires once worn down low, i've got v53 fronts and v54se or v54p on the rear work well there a different type of foam, stil soft but much better wear, either of those 2 work ok on the front too once worn small