*D1,*D2,*D3,*D5,*D8 are made from sprung blue steel and are more susceptible to rust, however they are less likely to develop kinks than the stainless steel kidneys.
D1 & D2 are the same in shape D1 is soft and flexible D2 is firm
D9, D1, D4, D5A, D6, D7, D10 are made of stainless steel and are very flexible (except D10 which is quite thick and rigid) & won't rust.
