The combination is rather vad för. It's not possible to translate What figure is it? with just vad, your options are either vilken ('which'), used as Vilken siffra är det? or Vad är det för siffra?.
vad can't be used on its own to mean 'what kind of' or 'what' as in 'which' (choice from a group). So you can say Vad äter du? 'What are you eating?' since that's an open question, but only Vad för mat äter du?/Vad äter du för mat? for 'What food are you eating?' (or again, Vilken mat äter du?) since here we're choosing from a group of options.
till in vara till för is a particle, meaning it's always stressed. We have a lot of particle verbs. The particle together with the verb creates a new unit with a different meaning from what the verb means on its own. Sometimes a small change in meaning, something it means something totally different. So particle verbs allow us to express more nuances of meaning without having a separate word for each and every one of them.
Basically vara means 'be' and vara till means 'exist', so with the preposition för, we get the meaning 'be for' as in 'be meant for' or 'be used for'.