CrocsSpecialist II Clog unisex-adult Clogs

How do you clean them? Mine are white and stained

Wich is the relation between size of crocs bistro and specialist ii? i use crocs bistro 9 with a perfect fit, may i assume i will be 9 in spec ii?

Does the heel strap fit over the top of the shoe if you don't want to use the heel strap?

I’m on my feet all day and have a bad back, how supportive are these?