Difference between organza and organdy petticoats...

I'm thinking of commissioning a petticoat from rinrinhime, but I can't decide between organdy and organza. Can any lolita tell me what they prefer, organdy or organza and how much layers are used for these petticoats? Pictures would be helpful. Also would my petticoat require more layers if it is not tulle? Thanks and sorry to bother..